I installed Office 2010 Pro Plus MSDN a few days ago with one of the two product keys that are widely available. These keys have now been blocked but I activated my copy before the keys got blocked... So the question is... If I rely on manual updates and don't install any future MS OGA update will this copy remain activated from now on or will it "phone home" at some point?
Maybe when you use some online tools like the cliparts gallery. Also, I bet you won't be able to install SP1 and later and some additional tools like the Calendar Printing Assistant.
Wait until somebody leak some retail key. Activate by phone and backup the activation files. That's much safer. MAK is easy to be blocked.