I tend to write and play this stuff a lot, and its damn good fun. Its hard to explain, but eventually you just get a feel for it. I write and play in 7/8 or 9/8 so often now I hardly notice I'm doing it.
For the more complex stuff (one of our songs has a section in 29/16 against 4/4) I remember the rhythms on its own and where its repetitions lie against the 4/4 beat - i.e the displacements.
In other cases I just remember the rhythmic pattern and keep playing that (Like in New Millenium Cyanide Christ or I)
Some of the crazier, less structured stuff I have problems with (like From A Second Story Window) - but I think thats more to do with the fact that they don't really write in signatures, they just deliberatly right oddly.
