Today I learned you can clear the BASH cache with hash.
Which is to say, BASH caches the full path to recently used commands, and sometimes that sucks.
If you install a new copy of a program with the same name but in a different directory (earlier in the search path), BASH might incorrectly run the old version. So, if you had svn in /usr/bin, and then installed a newer version in /opt/local/bin, you might end up pissed off. Natch.
You can see the current cache:
Or clear it:
$ hash -r
Or clear a single entry:
$ hash -d svn
Also: it rhymes.