I love the .22 round, and the Ruger 10/22 after growing up with it. I think the .22 is great for training on accuracy, trigger control, and not fearing the pop affecting the tendancy to jerk. And it is just so much fun and cheap. The rifle and aftermarket parts are dirt cheap, especially for such a great little rifle.
After having a hard time getting used to the trigger on the glock, I bought an Advantage Arms 22LR conversion kit, which has already paid for itself. The glock is so much fun to shoot in 22LR and you can really get used to the trigger *snap* after running 1K rounds through it. Your thumb will be sore for days, however, from loading the magazine so much.
Just keep the AA conversion clean and well lubed, otherwise the stovepiping will start to bug you. It is easy enough to do a quick field clean after a few hundred rounds.
I know this is a Rifle discussion but think .22 Pistols are just as fun and inexpensive.