The big problem Launchy faces in comparison with GNOME Do is lack of system integration. Thanks to its plugin system, you can search and play music in Amarok, or chat with your contacts in Pidgin, which IMO is the next step in launchers evolution (and well, what everyone dreams to do with their launcher of choice).
Still, it's nice to see more competition in the platform, even if Launchy developer seems to lack development time, considering the absence of new versions for a time, and how much it took to get a Linux version (he still has the Mac OS X version as well). I guess not every developer can release new versions every day ;)