there are plenty of books on photoshop out there, which may be the best way to go. Photoshop isn't exactly intuitive, but after some playing around, you can get the basics. I took a few classes on it, but I went to an art college.
even so, new versions are contantly being developed, with new bells and whistles. so essentially we're all continually "learning" with these types of programs.
I think a class may be a waste of money, unless you were using this program on a daily basis for work. If it's just for fun w/ your own photos and artwork, I think a book is the best way to go. There are many to choose from.... i.e., photoshop w/ digital photography, photoshop for dummies, photoshop [insert version # here], official guides, etc..