Yes, I have a similiar issue. I have a 2.53 Dual Core Macbook Pro. Ever since upgrading to 9.1.7, one of the cores is spikes every second around 90%, and the other core less frequently and around 20%. This is with any project open and basically idle, not doing any work at all. When I actually play my projects, or try to do any work, The mouse, and the video becomes very sluggish and sometimes unresponsive due to overheating. Reboot does nothing. Like an idiot, I didn't read all of the complaints about poeple having the same issue all over the internet before upgrading.
I can't work with Logic at all right now. I've opened a case with Apple, and plan to get in touch with someone when they are open tomorrow. Looks like I'll be going back to Cubase for a while. Way to go Apple!