(Graphs from here.)

It's too bad they don't describe their methodology. I'd be curious to see the flash ads they're testing against.

I ran the first flash ad I found in a standalone Flash player. It's not nothing, but it consumed less than 30MB RAM and around 3% of one CPU on my MBP 2.4GHz Core2Duo 17. The activitymonitord consumed more memory (though less of it resident) and CPU time. Meanwhile, with ads blocked, Firefox sat there doing nothing and consuming 15% of a CPU.