After having read that QuickSilver was no longer supported by BlackTree and has since gone open source, I noticed more and more people switching to/suggesting other app launchers i.e. Buttler and LaunchBar.
Is QuickSilver still relevant? Has anyone experienced any instability since it's gone open source?
Quicksilver is still alive and well. There are at least a couple of endeavours to keep it going, up to date and restructure and clean up the code base. Check out the code from Google Code.
As for launching apps, not even Spotlight comes close to how fast it is in Quicksilver.
Of course the real joy of Quicksilver is past just launching apps and using triggers, scripts and the many plugins. My workflow goes to a new level with Quicksilver. I'd be lost without it.
Update: Since posting this I switched and use LaunchBar for a while. This was during the time that QuickSilver seemed to be almost close to death. Loved LaunchBar and didn't need to switch back to QuickSilver. Recently though, I have left LaunchBar and have been using Alfred. I would highly recommend it. For me, LaunchBar and Alfred are pretty close. But, aesthetically and operationally, Alfred suits my tastes more than LaunchBar.