I have an Intel i5 iMac running OS 10.8.3 and have run the last few version of Bitcoin-qt on it. I have not seen any excessive CPU usage.
Hmm very strange. I have a i7 MacBook running 10.8.3
I tried v8 client up and nothing. Seems like other people have reported having the same problem from what some of my searches turn up.
I have just tried it on my i7 MacBook running 10.8.3
I can confirm that I am also noticing occasional spikes in CPU usage from Bitcoin-Qt (and from Armory as well), but it drops down after a while. Also, when bitcoin-qt is first run and scanning the blockchain, CPU usage is maxed out for the several hours it is doing that.
Now that you have me watching it, I am also noticing these occasional (seemingly random) spikes in CPU usage on my iMac (i5, 10.8.3).
Anybody have any ideas? Some kind of glitch in the MacOs binaries? I haven't noticed this in Linux (on the same Macs), but maybe I haven't been paying close enough attention...