I’ve used QuickSilver for a few years and I always considered it one of my essential applications. A few days ago I took advantage of MacZot’s deal to buy LaunchBar 4.
After using LaunchBar for a few days, I found that I prefer it. It’s a lot faster and more responsive than QuickSilver, which often gave me 10-15 seconds of spinning beach ball. I do miss QuickSilver’s hotkey actions which I used to control iTunes, so I had to go back to using Sizzling Keys for that.