My HP is 2 years old and is already beginning to slow down, though that could be due to all of the garbage I've accumulated on it- programs and files and such. No viruses or anything like that so far, fortunately. But I need to take a full inventory sometime soon and pare down what I've got- it isn't a huge amount, but some of the programs I run are extremely cpu hungry, and a few have background activity that use memory even when those programs are not actually running.
That might be contributing to the slow-down as well.
The battery doesn't last as long as it did when it was new, but with a full charge it can still give me a good 3-4 hours, provided I'm not running anything demanding (like tf2 maybe? i know, it's foolish, but i do that sometimes)...
The only serious concern I have for my laptop right now is the amount of dust and debris that I am positive has been building up in my cooling fan and beneath my keyboard. I really need to get some canned air and blow that stuff out. This is what killed my old Dell laptop- broke the fan and fried some of the more delicate components. I just keep forgetting to do it.