That really depends where you would see transactions working. Traditional transactions don't match well with the loosely coupled nature of SOAs. That's part of the reason the community (ourselves included) have been working for years on various extended transaction protocols, such as WS-BA. Those models tend to use forward compensation approaches, which allow for loose coupling of events/tasks, without requiring that you retain locks on resources for the duration of the "transaction". The downside is that you somehow may have to compensate for "dirty reads" if the overall "transaction" has to be undone. In some cases it may even be impossible to completely undo. But that's a trade-off.
If you go to the JBossTS pages (http://labs.jboss.com/jbosstm) you'll find lots of papers and discussions on this topic. JBossTS supports WS-BA, but the system is built on an extensible transaction core engine that can support a range of extended transaction models. We will be integrating this with JBossESB in some future release.