Generally SJAS 9 behaves fine, all problems I could easy reproduce have been solved by the GF developers - they are very helpful.
I have a current issue where SJAS seems to just stop - no log messages, but as Jan says don't base your decisions on 9.01 UR1, we have several instances and they all behave except one - but then it is serving millons of hits without any tunning...
When I get a spare second I'll investigate my own stablity problem - or get a support contract :)
I'd recommend SJAS/GF coming from JBoss myself, I choose SJAS at the time because we were moving from J2EE to JEE5, and at the time JBoss didn't have a certified EJB3 server. It has proven much easier to manage than JBoss, albeit a few teething problems.
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