Yes.. A lot of people are having the same problem.. You on 2.1 right? If you are like the rest of us, we are waiting on Apple to issue a patch.. Which they have given no word as to when they will be doing so..
Comes down to a bug Apple introduced in 2.1 that kills, or makes fetching unreliable at best, while the phone is asleep and on battery..
Here is the continuation thread of the discussion.
http://discussions.apple.com/thread.jspa?threadID=1767009&tstart=0
The link to the original thread is in the first message in the above link.. Word of warning, the orginal thread is very long..
Hope this helps..