Pros
You feel like you're part of something bigger than yourself. And depending on your VISTA program, you do have the opportunity to build community programming. There's also substantial latitude to set your own work goals and progress.
Cons
The reporting and accountability processes can be pretty lame. You have to file weekly reports with all kinds of numbers that may or may not be relevant to your job. Even though most VISTA positions are office jobs, you're not allowed to make money outside of the program. The vast majority of people I know rarely had official duties on evenings or weekends -- given the paltry compensation, we should have been able to earn money elsewhere. The program also doesn't seem to carry the same weight with future employers as Peace Corps, Teach For America, or military service.