When gmail first appeared I subscribed as soon as I could get my hands on an invitation. I forward a lot of mail to try it out.
Some months later, I saw that I could use gmail as an archiver for certain things, those mails you don't know if you really want to keep, but the problem was that now my gmail account was full of garbage.
I wanted to purge all mail from my account to start from scratch but there seems to be no way to do it easily. Clicking on 80 pages (8k message, 100 messages per page), selecting all and delete, was not an option.
So I wrote a script to login to gmail POP3 service, delete all messages, exit, and try again, until I got 0 messages on my inbox.
I now have about 10k messages in the trash, and those will be removed in 30 days.
In case you need to do the same, here is my x-gmail-expunge script. It requires Perl and the Mail::POP3Client from CPAN. Run it without parameters for usage, but it's really simple:
x-gmail-expunge.pl LOGIN PASSWORD.