I've unicycled for quite a while now, it's pretty fun although i haven't been on mine in a while. There is a unicycle equivalent for every practice of cycling so you can pretty much do whatever you want once you get it. I used to be big into the like street and trials riding. Being able to say you can grind on a unicycle is a pretty cool thing, haha. Most people get it in about 2 days of a couple hours of practice i'd say. And once you get that you abilities grow exponentially. After the first time you ride a block or so you'll prolly have simple straight riding down.

I'd say buy a cheap sun or torker lx from unicycle.com and go for it, they're pretty cheap and you can always step up to a nicer one once you figure out what you want to do.