Logging into dashboard is very slow

When logging into the Wordpress dashboard (v3.3.1), I'm noticing about a 15 second lag time before arriving at the dashboard.

I've tried deactiving all plugins and switching to the default theme but did not notice any difference.

When navigating to other areas of the admin, there is no lag time. When navigating the front end of the website, no lag time.

This is very confusing as it appears to be just the initial log in that has the issue.

I thought it might have something to do with me adding some code to capture the date/time the user logs in and add it as a column on the Users page. But since I deactivated that plugin and tested again, I didn't see a difference so I ruled that out.

Any suggestions are greatly appreciated. Anyone know of a way to spy on what's being called/queried during the log in process?