Speaking for myself, I don’t have Photoshop, so I don’t know how much I’d use it if I did. I agree with dblade that it’s nice to be on a level playing field for contests, and like Hammerknight says, it’s good to know if someone’s achieved a fancy effect with HM or with another program – mainly so I know if I can duplicate it, actually! 
I know zypping takes ages, but I think you get a lot of satisfaction out of it at the end, particularly by looking at the image before and after you zypped it, and comparing the two.
My 2 cents.
