I worked there part time from august 2004 - March 2005. I needed to supplement my regular full time career with some extra income for a few months.
I think the experience greatly varies from store to store based on management. We had some great managers at my store when I was there, but after I left I heard that some new managers came in that were real jerks to work for.
Personally, I liked working there. For me it was so much less stressful than my regular job, and I loved the animals. Its so great they allow people to bring their dogs with them.
Of course the downside to that is sometimes the owners dont clean up if thier pooch make a mess in the store. They think its YOUR job as an associate to clean it up.

Um no, thats why there are paper towel stations for you to use!
Anyway, we used to play rock paper scissors to see who got stuck cleaning it up
The pay was ok. Since I was coming from the corporate world, it seemed ridiculously low. But then I also applied at Borders and Barnes and Noble, and they were both paying 50 cents LESS an hour than petsmart. So I guess petsmart pay is good for retail.
Plus the employee discount was great! I had 2 cats when I started working there (another one by the time I left) so the discount really helped save me money on food and litter and toys.

My kitties were so spoiled!
feel free to PM me if you like.