Yes, Photoshop requires a lot of resources to run but it's definitely worth getting to know. I haven't found a graphics editing program that compares yet and I've tried everything I can get my hands on. The flexibility of Photoshop and the creative potential that can be unleashed by using the program isn't paralleled in any other product in my opinion. And once a person gets onto using custom brushes, actions and patterns it really opens up a whole new world of design possibilities.
Gimp is pretty good too.