Installing gems is usually very quick on my computer … its the accompanying ri and rdoc installations that slows everything down to a crawl.
There’s an easy way to stop ri and rdoc installs on Windows.

All you have to do is go to
C:\Documents and Settings\All Users\Application Data\ on Windows XP
or
C:\ProgramData\ on Windows 7

create a file called gemrc

then put in the following
gem: --no-ri --no-rdoc

Hat tip to this Stack Overflow comment, give the man some more upvotes!