The title may well qualify as an oxymoron, but I'm sure Mark Little disagrees:
So we originally created a student project to dust off the old REST transactions protocol(s) and implement them today. This started life before JAX-RS (again) but by the time something really happened JAX-RS (and RESTeasy) was around. Michael from the JBossTS team took this work on and did a great job. It's not finished (only the atomic outcome protocol has been implemented so far, for example). Plus the protocols haven't been changed at all since they were created back in 2000/2001. So there are still some things we need to look at and more interesting work ahead.
If I understand the protocol correctly, transactions become resources in their own right (which I like). Even though I have some misgivings about the details of the protocol (the verb-style resources, 401 instead of 405, lack of hypermedia usage, lack of discoverability …), I'm sure these could be addressed – it really comes down to the question of whether or not distributed transactions are needed or not in a REST/HTTP scenario.