Opening finder instances extremely slow in browsers and quicksilver since 10.6.7 update
Did you update to 10.6.7 using the Software Update utility? Or did you use the Update Combo?

It's not unheard of for the Software Update utility to muck things up. The advantage of using the Update Combo is that it rewrites everything, as opposed to doing a 'delta' upgrade.

It should be noted that the Update Combo package is now weighing in at over 1 GB.

You won't do any harm, and you may fix things, by running the Update Combo linked to above.