Two months ago I raised ticket 1543 regarding the fact that from time to time, after having cURLed an update request, then I got no response nor any timeout although timeout options were set for cURL. Twitter Inc. suggested to discuss this here.
I might have a clue : as a last chance we updated our cURL and libcurl to 7.20.0 (we were using 7.18) and since then ( that's nearly 6 weeks, this didn't occur again (it used to occur at least once every two weeks). Can libcurl users have a try ?