Mystery solved! (At least, in my case).

I have a couple of hotmail accounts that access via Outlook as http accounts.
Well, it turns out that Outlook keeps building its .pst files for these
accounts, even though I've deleted the messaages.

Just close Outlook and delete these .pst files. Outlook will automatically
rebuild new (and much smaller) ones.

One of these puppies was over 9GB in my case.

Now all is good again.

url:http://www.ureader.com/msg/10768245.aspx