Lydia is the housecarl you get from from Whiterun right?
Everyone goes on and on about her but she died fairly quickly to a swarm of falmer. All my followers have been pretty weak. I even oufitted a sellsword in full Dwarven Armor and he got knocked off a catwalk in a dwemer ruin. Followers so far have been nothing but baby sitting for me really. I am on my second character now, Khajiit assassin, and I don't think I am even going to bother with them this time. Although there are times I could use the help because I am very weak in open combat, I still don't think it's worth all the trouble.
It all depends on how you play, and how well you learn to use them properly. They can do a lot of annoying things, no doubt, and they aren't intended to do all the work for you, especially at lower levels... but they can save your life in a lot of situations, when played right. One thing that does hold them back, is that they don't level up with you as you progress, for instance, if you get Lydia at level 6, she will stay that way and continue to be quite weak and easy to kill, even as your char becomes much more powerful later on, and goes up against much more powerful enemies. Why they didn't let followers level up with you, I have no idea. But if you are on PC, you can fix this problem by following the instructions in this tube: http://www.youtube.com/watch?v=kkxVqveNDVs
Very handy.