I had noticed in one of the previous post-Beta interim builds of Windows 7 that ESET NOD32 was throwing up an Action Center message to the effect that it was incompatible with the way security software communicates its status; previously, NOD32 worked just fine. In the RC build, this has been formalized with an appearance by the familiar Program Compatibility Assistant window shown here. There's no fix as of yet, but I suspect this change will affect more than just NOD32. I will check.
I don't see any documentation about what's changed with regards to security software, but I'll ask Microsoft during our Windows 7 RC briefing early next week.
UPDATE: I should note that this is NOD32 3.x. I've been told that 4.0 works without complaint.