My Inspiron's battery last me about a year, which is all I expect from a laptop battery, especially when I'm killing it royally seven days a week. My MacBook's battery died in a similar timeframe. It didn't make it to the cycles advertised (1000 advertised, I barely made it past 400 before my charge was seriously dropping) so Apple replaced it.
You can't go wrong with the unibody design. It's ridiculously solid. The "plastic" MacBooks aren't plastic, they're polycarbonate. They're pretty much indestructible, and if you manage to destroy one through everyday use, Apple will probably hook you up.
I still stand by Inspiron if you can't afford an Apple, though.
EDIT -
One thing to consider though is that with Apple, you don't need a new machine every year. I've always had a computer for about one year before getting a new one (usually due to epic failure of the old one). This one still is very on-par with my needs and I'll probably have it until at least the two-year mark.