I'm experiencing unmounting problems with OSXFUSE 2.5.2 but not 2.5.1
In my tests volume gets mounted fine, then accessed and unmounted but with 2.5.2 unmount takes a long time and usually comes with memory violation error.
It seems that the volume is unmounted fine and still some extra work is done in the background.
The last thing I could see was getattr on / although that's probably irrelevant.
To unmount I'm using umount -f /Volumes/myvol command.
I think there were some changes between 2.5.1 and 2.5.2 related to race condition in unmount?
Problem is very reproducible. I'm on Lion