Rebecca has been wanting to wear underwear recently, so a couple weeks ago I started letting her wear underwear unconditionally. The previous couple weeks had seen occasional underwear use as a reward for using the toilet. Once she started wearing it constantly though, she was able to figure out what was going on much better. The first day was 'Aaah! I'm going pee!', which was about where we were with the occasional underwear use. So it was more of a wimpy cloth diaper than anything else. After a day or two or more, I can't really remember, she figured out how to stop going pee. Then it was 'Aaah! I'm going pee!', followed by a small use of the toilet. And it got better pretty quickly from there. There are still wet spots in her underwear half the time, but they've gotten smaller, and, hey, half the time.
I wasn't sure about the whole 'just use underwear' scheme, but it seems to have worked pretty well for us. The first days we spent a lot of time in the linoleum kitchen, or other easily cleaned locations, but since she was the one who wanted to do it, it all worked amazingly quickly. The first week was wet, but there's so much wetness that comes with babies already it wasn't really a problem. I'll take urine over projectile vomiting or diarrhea any day.