Just wanted to update everyone. Apparently there is a compatibility issue with the 5.1 firmware and certain routers. This is my conclusion after 2brand new apple tv's, latest models.
If you read my previous post you'll know that I could get it to work via wireless but no luck with ethernet cable connected. In my case one I switched my crappy Rogers supplied cable modem/router/wireless access point over to bridge mode and connected my trusty D-Link dir-655 to do the routing and wireless, everything is now working perfectly with the 5.1 firmware in the Apple TV.
The SMC Rogers device has very few router settings that the end user can tinker with, but that seems to be the problem. Anyway, after switching to a decent router solved the problem for me anyway.
I think this is still a fault on Apple's part for not testing things properly, despite the crappy all-in-one modem. The fact does remain that 5.0.2 works just fine on that device but the new software doesn't.
For everyone else out there with this issue, give that a try... Even bypass your router all together (temporarily) and see if it works for you. May not bea feasible solution, but gives you an idea where the issue may be in your particular case.
Cheers.....
D