It seems that it's always addressed in an update, but SMB performance on a Windows network sucks.
It takes 20 seconds or more for me to see the contents of a Windows network folder. In Windows, it's nearly instantaneous.
Of course, it could be a multitude of problems with my particular installation (isn't it always?), but browsing network volumes seems like a low level OS activity that shouldn't be affected by, say, a Star Wars screensaver I have installed.