Stop spacebar triggering quicklook when using Quicksilver
The default spacebar behavior was changed from “Normal” to “Smart” a couple of years ago. Users that had chosen a setting explicitly were unaffected, but if you had never picked anything, the new default took over.

You can change it back by going to Preferences → General → Command and looking at the Spacebar behavior setting.

Having said that… You should never need to type a space when searching and you should never need to type that many characters. The main feature of Quicksilver is that it lets you find things with an abbreviation that makes sense to you, and doesn’t require typing full names of things.

To find Activity Monitor, a m should be enough.

I encourage you to try the Smart behavior. It’s quite a time saver. This is what it will do:


If the object has children, show them (unless it's a text file)
Jump to the third pane if the current action requires it
Quick Look if the object supports it
If user is holding Shift, go to the parent (same as left arrow)
Switch to text mode
If in the second pane, select the first action that takes an argument in the third pane