I actually like reviewing, and I say do it!
Reviewing forces you to read papers carefully, and to broaden your view of your field. This seems especially important when one is a grad student. I am perhaps atypical as a reviewer, in that I spend huge amounts of time reviewing papers, because it's exciting for me to see all the great work other people are doing! I know it makes me, if not a better mathematician, then at least a more widely read one. So I write maybe a few dozen reviews for Zentralblatt each year. The nasty part is when you get sent papers to review which are rubbish, in which case (I think) you do a community service by pointing out why that is so.