Not sure if this is related to your problem ... but we too have had JBoss hanging during web requests and also other servlet related activities.
Had to use JProfiler to help us work out what was going on. It revealed that log4j (yes amazing as it seems) is causing blocked threads.
You can refer to http://issues.apache.org/bugzilla/show_bug.cgi?id=24159 in bugzilla for a rundown on the problem.
Whilst we are not 100% positive that this is our problem I am in the process of turning off the logging to see if the problem still occurs. Unfortunately this can take anywhere from 10 minutes to 8 hours of testing as the deadlock is difficult to isolate in such a big system as ours.
Anyhow - hope this helps and let us know how you get on.
The log4j folk don't want to fix this. Could you post a thread dump and explanation of your problem to the bug. Thanks.