It can be a challenge to focus, but then any lens manually focused can be a challenge. The 50mm is very light on the touch though so I usually stick a piece of blu-tac or similar against the focus ring and lens body to add a bit of resistance. Makes the world of difference. Then again so does DSLR Focus
(Unfortunately I don't think it works with the 40D)
I've read a few reviews of the 100 and most seem to be pro rather than against. Here is a variety.
http://www.fredmiranda.com/reviews/s...php?product=33
Don't know how unbiased this one is with all the adverts at the bottom
http://www.photozone.de/8Reviews/len...00_2/index.htm
But for $600 I think you will be hard pressed to better it, though the 100 macro (not the soft focus) it a damn fine lens by all accounts