Infrared shooting with my RM-72 filter, *istDS and 31/1.8 Limited.
I've been intimidated by infrared for a long time, but I think I really got comfortable with it after a gazillion stupid, beginner mistakes (like leaving the camera on 1600 and JPG). The RM-72 filter filters out the visible light, giving the infrared light an chance to get to the sensor and make beautiful, surreal pictures. Its a little disconcerting to not be able to see through the viewfinder, but with still subject matter and digital it doesn't really matter because you can always just make adjustments and reshoot. The autofocus seemed to work wonderfully, though at f8.0 and above, I can't really critique too finely.
I was also shooting with the same lens and same filter on the (film) K-1000 and Ilford SFX film. The guess and adjust method doesn't work on a manual focus film camera so not only did I not get help in composing, I also had to see through the viewfinder (and through the filter) well enough to FOCUS! Being the dork that I am, I threw a shirt over my head and the camera, pushed my eye hard against the metal eye piece, and thanked my stars that I do not really have to wear my glasses to see.