Regarding MicroSoft's "SourceSafe" product...
It polls! There is a notable difference in performance on a machine when you have it open. Flip to the performance tab in NT task manager when VSS 4.0 is open and watch your CPU usage line climb to a high plateau. -- MichaelFeathers
Regarding the polling, that bug has been fixed; see KB article Q154469, "FIX: Visual SourceSafe 4.0 Increases Processor Usage" at http://support.microsoft.com/support/kb/articles/q154/4/69.asp
If you have to use VSS and VisualStudio over a dial-up line, try "Gnome Hammer", available at http://www.gnomehome.com/, which forces some of the processing into the background, speeding things up tremendously. --KatyMulvey [this web page just has a single line of text and no links -- nothing about "Gnome Hammer". Has it gone offline ? Is this the wrong URI ?]