CPU B using more power than CPU A?

The balance of processor usage between cores is never the same. If you are using an app that can only use a single processing core then it will increase the load on that cpu thus increasing the power draw on that core.

 

On my 2009 MP the A CPU usually runs hotter and uses more power.

 

I've found it's best to not stare at the sensors display in iStat Menus too long. You start getting paranoid. (Although it does tell you interesting things about why battery life mysteriously goes away in Snow Leopard)

 

I get way to obsessed with the stats that iStat gives me, the problem is that I also set up the iPhone app so I can see stats wherever I am.

 

The OS frequently switches the core an application hogs to balance thermal loading of the die.