Very simple, very fast, very nice.
I use both this and Quicksilver. Quicksilver is obviously a lot richer in options, but also takes longer to learn to use, and can be slower and less effecient when you simply want to open an app it hasn't 'learned' abbreviations for yet.
It's a taste thing. I rely on Quicksilver more and more, but my wife, who values clean simplicity more than bells and whistles has happily stuck with ABC Launch as her default launch app. (The fact is, either is wonderful as a free app).