If you're looking to learn how to use Photoshop or trying to improve your skills, I highly recommend checking out creativeLIVE's Photoshop Week. They go over a ton of material in 5 days and you're bound to learn something new even if you're a seasoned Photoshop vet. All you have to do is create an account. They rebroadcast all the workshops later in the day if you're unable to see them the first time.
It's honestly helped me a lot after checking it out last year and Kotaku's 'Shop contests provide a great outlet to practice regularly.