The closest agility is in my city, twice a year (three times if I have a dog for the novice/open only trial) but other than that, I go anywhere from 45 minutes to three hours away to trial. The furthest I go is Louisville which is four hours and that's only once a year. But it's under two hours to Indy, around two to head towards Chicago if I wanted to (generally I don't), three-ish to the St. Louis area. There's a place in Southern Indiana I go to, that's about three as well.
I don't feel like three hours is far away... but having to go three hours for EVERY trial would be super annoying! I'd probably still do it though. I actually like highway driving. =P