We'are also using JBoss and running some complex workflow processes on it. Of course I've been also confronted with many problems during the development phase. But none of them were "JBoss problems"... the system is running stable since june 2007 (until today).
We are experiencing issues with the Form Server Submit Form capturing the data from our form and placing that data within the workflow's document variable. Adobe tech is trying to figure out why, but so far no success.
Plus I hear a lot about Websphere from both our consultants and Adobe tech so I was curious.