I am on the PC, but have never used console commands much... and not at all with Skyrim yet. Is there somewhere I can find a listing of them? hmmmm... perhaps there's a mod...?

Nope. Lydia dies well and often, if you don't make keeping her alive a priority. Then it's Reload and do it again time, if you really don't want to lose your Lydia.

It's weird how so many players actually keep Lydia. Its almost like she is synonymous with the word follower. There are so many followers to pick and choose from, so why do people keep the first one they come across?

Google uespwiki and console. It will give a list of commands, effects, and the language to phrase them.

If you are on a console you are hosed unless they patch it so Lydia levels with you.

On a PC Lydia is a studdette if you do the following.

Tell her to leave and then hit ~
Click on her and type disable (she goes poof)
Close the console
Open it again and type enable.
Shes back.
Tell her to follow.
Shes now your level.

As for her dying, no she does NOT simply die because shes hit in normal combat. Every Lydia death I've had can be traced back to me, either a spell or a hit or a shout. I found out the hard way that using unrelenting force on a boss while Lydia was on her knees will kill her. I've seen her in a fire trap SLOWLY crawling out of it on her knees while surrounded by flame. I've seen her take arrows on her knees (dont' say it) from guys who could one shot my mage. EVERY one of my Lydia "oh crap she died" was my fault, though sometimes I didn't realize it at the time. You have to be careful with fireball, runes, etc. Even power attacks because she does like to jump in front of you and the rather odd 'range' of weapons means it easy to hit something that it doesn't look like you could hit on screen.

I can only assume that this might depend on player difficulty level, like it did in Fallout New Vegas, because most of the time she does the whole "down-on-one-knee" thing.

However....

There do seem to be some quests or dungeons where she can die, and not be getting caught in my crossfire. This seems to be true of all followers, as Iona (?) the Riften carl was killed while I was fighting someone else. The manual supports the view that followers can only be killed by you - including things like area effect spells - but in my experience there's either a bug or it's not that simple.

Sounds like your play-style is similar to mine. The only parking problem is if I accidentally park her too close to the action with no door between. Then, even if I've commanded her to stay, she wades in anyway, usually alerting every baddie in the area to her and then my presence. She definitely can't handle many of the resulting attacks my Lvl 26 Battlemage character can handle.

I learned the hard way not to use a Chain Lightning staff around her, even though she was behind me and I was firing at a mob of spiders in front, the lightning chained to her and killed her stone dead. Paid a lot of gold for that staff, but now, for Lydia's sake, it's just a wall decoration.

This.

Plus Lydia is by default the weakest follower you're going to meet (unless you decided to skip the first few quests and run off into the wilderness) by virtue of being the first follower you get.

Maybe it's time to let go man, sounds like you've outgrown her, she simply isn't a talented enough adventuer to keep up with you anymore.
May I suggest checking a few inns for mercs?
500 gold flat fee and they are usually pretty tough, plus if they die it doesn't break your heart (and you can usually recoup the fee by stripping and selling all their gear).

Lydia is a glorified butler, leave her where she belongs, baking sweetrolls in Breezehome and go get yourself a real follower.

Just left her on your house at Dragonsreach.Lydia is weak because you found her at the beggining of the game.And companion's are level-based.So if you find a companion at level 1 he will have everything that a level 1 player have.

Its better to upgrade her with another thane and retire Lydia. Companions are supposedly fixed at the level you first meet them. So if you meet Lydia as lvl4 character she will always be a lvl4 npc. Later when you can afford the house in Solitude you gain Jorvis as a thane who is basically a Lydia clone but with a different voice actor. I only picked her up as a lvl30 character so she started at that higher level and remains a good companion to keep around. Lydia meanwhile has been demoted to house-keeper.

The official Strategy Guide says that followers level up with you.

The official Strategy Guide says that followers level up with you.

I like Lydia. She's totally loyal "unto death". But how do you keep the girl alive? It seems I'm spending huge amounts of gold, and many extra hours of time, just trying to keep my loyal Lydia alive and with me as I wander. It's frustrating to look back and see her running in place, stuck behind a tiny rock I just bounced over. No cross-country exploration for Lydia, it seems, I can't take her most places where roads aren't involved. Heaven forbid the grade is too steep or the terrain too rocky, no matter I can handle both.

The Lydia problem gelled when I actually chose Ebony over Glass crafting as my Smithing perk. I needed Glass for my Light Armor character, but Ebony might better help keep Lydia alive. While it's true you have the choice of leaving Lydia behind at the house, you pay for it. Whenever I go into my bedroom, there she is, sitting at the little table despondently munching on a hunk of bread, casting morose glances in my direction, obviously crushed at being spurned by her thane. Whatever happened to "they also serve who only stand and wait" and the steadfast attitude that goes with that philosophy?

As the final straw, when I take Lydia with me to work more-or-less as a pack horse, the girl can't carry much of anything, especially now that she's all in Ebony. If I take her into a dungeon, she runs ahead into the fray, intent on killing or being killed. Discretion is definitely not her longsuit. So, she stirs the hornets' nest and sets them all on me, or she dies and sets them all on me. Great choice. I park Lydia outside if I plan on a bit of finesse in my play-style. Further, how to fill soul gems with my over-protector around? Before I can get my bow aimed, she's killed the critter. Frustrating.

I have some suggestions that might actually make Lydia and her ilk an asset: 1) Lydia (or any follower) should be able to maneuver any terrain you can maneuver; 2) add the command "Stay behind me!", which will make her stay... well, you know... BEHIND you; 3) increase her carry-capacity, wearing Ebony shouldn't max-out her weight-limit; and 4) if you no longer want her following you around, no sad-faced, overly-dejected moping when you release her to stay and guard your house.

Like I said in the beginning, I like Lydia, she just needs to be something other than a huge drag on my game... either as someone, incapable of carrying much, who I must constantly spend time, gold and personal safety on to keep alive, or as an emotional guilt-trip, should I give up and leave her at the house. How do either of those things enhance game-play, Bethesda people?

They are shocking... bugged. Check out my console fix in this thread. Lydia is a beast IF she is leveled with you.

A beast! Yes, that's what I want her to be. A carry-a-lot, monster-in-a-fight, stay-outta-my-line-of-fire baddie-bane...

uh... how do you go into console mode?