Just a note to other webmasters out there: the Google bot does not respect the moved permanently 301 HTTP response status and continues to request the resource.
I have noticed this in my Google App Engine logs when trying to remove the redirect after being in effect for at least 2 months. I know it may sound weird, but yes the Googlebot is still ignoring the 301 and requests the permanently moved resource every 30/40 minutes.
You can identify the Google Bot by checking the the User-Agent for the string Googlebot/x.y (current version is 2.1, so the User-Agent fragment is Googlebot/2.1).
I am wondering what will happen with the URIs returning 410 Gone. In fact I'll just try it out in the upcoming days.
Not far ago, I have written how Google Desktop is breaking privacy by trying to submit data even if I have set it up not to do so. I cannot stop wondering:
mattcutts: @al3xandru, we can trust the 301 redirect, but it still makes sense to periodically check the source page every so often.
I don't think this is the correct behavior though. I'd be expecting this behavior for 302 (Found) and 307 (Temporary Redirect) which both are used for marking temporary redirects, but not for 301 moved permanently.