I'm managing a small network with Small Business Server 2008 and 7 clients running a mix of Vista and XP. The server and clients are all running McAfee Total Protection Service for malware and spyware protection; the clients are also using the McAfee firewall and browser protection features as well.
The McAfee TPS product, which is managed from the cloud, is shown as functional in Windows Security Center on the clients, but the clients are not reporting their protection status to SBS. The SBS Console lists "Critical" status for all clients for both virus and spyware protection, and says that the clients "cannot be queried."
This Usenet thread suggests that WMI traffic is being blocked, although WMI Provider Host has been granted access through the McAfee firewall on the client (the Windows firewall is off).
These clients formerly ran AVG antivirus and they didn't successfully report to SBS then either, which makes me doubt that it's a vendor-specific problem.
Update: Alejandro Campos Magencio's most recent comment on this blog post suggests that McAfee may not be using Microsoft's new super-secret API to report security status to the server. I have a question in to McAfee support about this, though I'm not holding my breath.