Or you can tell Quicksilver (in the "Command" part of the Preferences) to automatically switch over to text mode if what you're typing doesn't match anything in the catalog. So if you type the address of a site you've never been to, it will automatically switch to text mode and automatically recognize the text as a URL, so the steps are:

1. Invoke Quicksilver
2. Type address
3. Hit Return

…or you can do that complicated crap with creating shortcuts and writing Applescript and typing a lot of stuff to invoke it. ;)