Pros
It's a fantastic networking opportunity, particularly if you're in college. A lot of the tax pros have "real" jobs outside of H&R Block, providing a great opportunity to learn more about some the fields in your geographical area. Free tax return was kind of neat. If your taxes are relatively straightforward though, then it's just a wasted perk. Working in a mall provided great 'scenery' if you know what I mean.
Cons
The pay is awful, and there's no real incentive to move up in the company because they're closed 8 months out of the year. Even if you move up to tax pro, you still don't make very much. A lot of mandatory training and seminars for a four month job. Occasionally cranky customers who don't understand anything about taxes.