KB2761451 can prevent web access to the Netgear Genie pages if you are using a Netgear router. Not sure yet why this is, but the simple answer is to put the Router URL into IE9 using compatibility mode.
KB2750841 adds some IPv6 functionality apparently. However if you use OpenDNS this can cause the repeating pop up in the right hand side of the task bar asking for additional log in details. Plenty of comments on the Internet if you google KB2750841 - esp for gamers. My simple answer has been to to revert to using BT's DNS but if anyone know the answer that would allow the continued use of OpenDNS without the pop ups I'd love to know it.
Both issues have been flagged up to MS who are apparently aware of them (so why don't they resolve them before slinging out the updates I ask myself.........)