Positive - You get to see a lot of orchids, and you learn something new (or many somethings new) at each show or judging you go to. I've found that (at least in my center and the surrounding ones), almost all of the judges are great people, friendly, and they would sell a kidney to help you out. Orchid societies are great hosts and it is fun to hang out with new people at shows and eat and talk.
Negatives - You get to see a lot of orchids, and you end up buying more... You tend to bring your better stuff for judging, and get awards, which costs more. But seriously, it is a major time and money commitment. You are expected to go to every monthly judging in your center (barring a really good excuse) and several shows in your region. In our center, the absolute minimum is four shows, but that would get you laughed at. Most judges do at least 8 shows a year. It costs money for gas and lodging (some of that can be used as a tax deduction, but that only helps a little). You will be expected to do some homework, which (in our center at least) isn't awful, but it can add to your time commitment. And there are a few blowhards and idiot judges (usually older ones) who can be a 'treat' to work with. Few and far between, but you should work on a tough skin anyway.
You will be a student for a minimum of 3 years before your votes even count... Then probationary for a minimum of two (I think two?) more years before you are a 'real judge'. It really is substantially like graduate school. So, it is a commitment. But, you can stop at any time, if you decide you don't like it.