I've done four in the past four years, will do 2 more in 2011. I can say I'm very glad I lost that bet on Fourth of July weekend 2006 and started.
As far as training, there are so many ways to do it. For the last one, I took the one straight out of Runner's World magazine, made some small changes based on my schedule and other activities and did the best I could.
Some running clubs have programs, others just organize group runs -- and this is the one thing I would encourage more than anything else. I ran essentially by myself for 3 1/2 years, but started with the local running club (to do an interview, of all things) and enjoyed it thoroughly. I still do plenty of runs by myself, but I always look forward to a group run now. Granted, we all get strung out during the run because we're all at different paces, but that's OK. Good to talk, say hello to new acquaintances, grab dinner afterward.
The one thing I can't stress enough, though -- listen to your body. If something feels funny, slow down, take a small break. If it still feels funny, shut it down. While I am far from the fastest person out there, I've had zero injuries and enjoy going out to run every time. That's been the whole point of all this. I'm not fast enough to be a BQ (and probably won't be until I'm 60, god-willing I can still run then), and I'm OK with that. But I just broke four hours for the first time, and now I want to get down to 3:50.