Witless uninstall #1 (perfect for those crappy tarfiles that exact everything into the current directory)

    tar -tf tarfile.tar | xargs rm

Witless uninstall #2. Find a file that you changed just before "make install" into the wrong spot (usually config.log is a good candidate).

    find /bogus/installdir -newer config.log  | xargs rm

Yes, this is totally unsafe. But it's an abuse... so, there you go