In my case ... a lot!
I did the IMC test on a crappy day and the weather reduced to below minima before I finished. The test had to be called off and I could only be given a partial to take into account the area of the test that was done. Unfortunately, money, work ect conspired to stop me returning in the time allowed and the partial lapsed. I never went back to complete
That said, I enjoyed the training, found flying on instruments a doddle, but not exactly fun. As it was only intended as a safety feature and my flying tends to be in PFA types anyway I haven't felt the need to do it again. Maybe one day when I strike rich! lol, I'll re do it all
IM