I have made a patch to configure the atxfer timeout in features.conf. The default timeout is 15 seconds, a bit low I think, so I made this patch.
You can find the patch and install instructions here (English and Spanish):
Works with Asterisk 1.2.4, 1.2.5 and 1.2.6
Hope you find it useful. Thanks.
Update 20 May 2006: Works with Asterisk 18.104.22.168 too, including with bristuff patch.