I used to be a heavy user of Quicksilver but since it was effectively abandoned I moved over to using Alfred. For the most part it goes above and beyond what I was able to do with QS and I love it. There are a few things I miss (or, at least, can’t figure out how to do) like displaying phone numbers and messages in big type as an overlay.
In the last few days I noticed that the dialogue box would hang on my first search after invoking it. Subsequent searches (if I didn’t dismiss it, but instead cleared the text and started a new search) were as quick as I would expect. Some googling didn’t reveal much, so I decided to rebuild my Spotlight index using these instructions. Seems to have cleared up the problem.
[UPDATE: This issue has since been resolved and addressed in another post]