Once it loads it is quite responsive, however the mouse & cursor has alway been buggy due to old windows never being designed for touch screen use. Personally I have always preferred win95 as it has a smaller OS footprint and does not freeze half as much.

As for its usefulness? Well if you have a specific windows program that you need and does not require too much mouse interaction then it's handy to have. If you don't and you can find a more suitable program to use in easy debian, then it is more of an curiosity that you can mark it down as another cool thing the n900 can do.