As any good web developer should, I have all errors generated by my websites logged and emailed to me. I've been seeing a number of 404's lately with the following request:
/MSOffice/cltreq.asp?UL=1&ACT=4&BUILD=5606&STRMVER=4&CAPREQ=0
If you are seeing this in your web logs, its because your users have Microsoft Office installed, and the discussion bar turned on in IE. IE is querying the server to see whether it supports web discussions.