WS-Reliability became an OASIS Standard. Now we have WS-ReliableMessaging and WS-Reliability in the same area in he same way that other specifications. The two proposals addresses the problem with similar perspectives. I really prefer WS-ReliableMessaging. I think that is a little more simple and can be combined more easily with other specifications like WS-Policy, WS-Security, etc. In the IBM SOA developer center you can find this article that explains some of the main concepts of WS-Reliability. A months ago a wrote this article that explains the WS-ReliableMessaging implementations provided by Indigo and Systinet WASP.