The plugin stops checking immediately, and on the options page the status reads:
"No broken links found.
No URLs in the work queue.
No links detected."
The only other anomaly is in the debugging status, it says "You have an old version of CURL. Redirect detection may not work properly."
I have a custom theme based on Kubrick that doesn't use widgets. I just upgraded to WordPress 3.0, before I did the plugin would display a php error page with "delete() on a non-object" error" and show the same "No links detected" status in the options page.