I've painted two shower stalls that get water on a regular basis and they've held up well. The trick to painting tile is the products you use, and the prep. You have to clean the tile well with something like STP(your paint store will have what you need to wash it with). It needs to be scuffed up with a sanding(no you don't have to take the shiny surface off the old tile, just scuff it). You *have* to prime it with a high adhesion primer(your paint store will have it).

You can then paint it with whatever you want for a finish. You can buy "glass finish" paint if you want it to be real shiny.

I was really pleased with the way mine turned out. You will be painting over any grout when you paint the tile, but it is a cost effective way to change the look of the tile. I did not mind the look of the grout painted over at all, in fact I think I like it better.