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?