My site currently gets very few hits from it (about 40 per week), but all of those hits are directed to a retired hostname which automatically supplies known bots with 301 redirects to equivalent URLs on its new hostname (other clients get a “300 Multiple Choices” so they read the page, followed by a 5 second Refresh if they don’t click the link). Googlebot and Yahoo! Slurp understand them properly (they immediately rerequest it from the new URL and update their index), but when Twiceler receives a 301 response, it simply gives up and goes to the next page in its list without ever following the redirect.

I don’t know if it’s smart enough to follow temporary redirects (302 and 303), since I don’t use them anywhere on my site (except for login forms and such, which bots aren’t going to follow).