CS5 has a lot more "power user" features. The general editing abilities are similar, but you will have access to some important tools that will make editing things a lot easier:
Curves: Very good contrast adjustment tool. You can also use it to control colors seperately, which is a good way of working on B&W photos (not great for color photos though!).
Additional editing tools, like liquefy (useful for portrait photography if you're in to editing the way people look a bit).
The RAW converter is much better than it used to be, and the noise reduction in it is much better too.
Elements doesn't really have any batch editing options, whereas CS5 has a lot, so if you want to run a bunch of images through some standard stuff, it is much easier... once you figure it out.
There are a ton of PS
tutorials on youtube of variable quality, I would recommend you peruse through some. This one seems like a decent place to start (he babbles for a couple minutes at first but then gets in to them pretty quickly at 3 minutes or so):
It may not be for CS5, but don't worry about it. There are tutorials for stuff CS5 does too.