As much as I'm sure Google would value your opinion, I'm sure the people there have considered everything. They wouldn't have implemented this design unless it was the most energy and cost efficient design they could possibly think of.
Thats why Ben Jai gets paid a huge sum of money, and you're posting on Slashdot..
We use Sophos at the school I admin with the enterprise console. It is by no means the greatest antivirus out there, but it does the job. It doesn't intrude on the user, updates itself quietly and efficiently and you can manage clients well using the enterprise console. I believe its fairly reasonably priced, but we get a discount being educational (they sell heavily to schools)
Just make sure you only get the endpoint AV and not the bundled firewall - that really sucks
"May your future be limited only by your dreams." -- Christa McAuliffe