My Macbook Pro was getting slower and unresponsive. Then, Quicksilver started to crash. Thanks to some other blog, I found the clipboard module was trying to store huge clipboard data, resulting in a 930 Mb file. To fix it, stop Quicksilver, remove ~/Library/Application Support/Quicksilver/Shelves/QSPasteboardHistory.qsshelf and restart Quicksilver. My MBP is now fast again.