This is great. CPU is higher than native, but not too bad (especially considering it's an initial release).
I was getting 10% each on Chrome and a Chrome Renderer process. I paused to switch over to Cog to check its CPU usage, then switched back and it was hovering around 6%. For comparison, Cog spiked to 15% for a second then settled in at around 1%.
I'm on a 2010 Core 2 Duo MacBook Air.