We have deployed a number of Web Services backed by ejb3 business objects. We are very happy with the load we have been able to handle. We have scaled past 50 concurrent users with little trouble. We have experienced that the SOAP stack is the bottleneck in our system as the ejb machines never pegged any resources. However, we are not using ejb3 persistence as most users are. We have opted for stored procedure backed entities and have handled deadlock situations in our procs. I have heard about deadlock problems when using the full blown orm ejb3 solution, but for the reason mentioned have not experienced it myself.