Backstory is that I ran Windows 7 in a VM without any anti-virus while doing some evaluation, and I was impressed by how sparing it was of resources.
Then I installed the RC on my (underpowered old) laptop, figuring it would be a good replacement for Server 2003 (which is resource efficient but not exactly designed for laptops).
The RC used somewhat more memory -- it appears to be able to adjust its memory footprint depending on the host hardware, which is cool -- and a ton more CPU.
The CPU usage was suspicious because it's rare to find software that consistently pins a CPU with actual work, and because the usage was high priority -- coming from kernel space or a library tied tightly to kernel hooks. It was also suspicious because Microsoft plans to sell a version of 7 on netbooks, which are even more underpowered than my two-year-old bargain-o-matic laptop.
Turns out AVG, generally a fine anti-virus product, struggles with Windows 7 and often insists on every available CPU cycle, while the end user sits there wondering why context menus won't even open anymore.
After a bit of Googling, I removed AVG and installed Avast, and 7 is screaming along on the laptop now.
Note the retroactive Windows 7 hardware subsidy: this laptop was discontinued by the manufacturer in '07 because it shipped with Vista Basic but proved so slow as to be completely unusable in that configuration. The new OS basically injects value into the old machine.