Mac slowing down problem

Check for background tasks in the activity monitor which might be hogging the CPU.
Also do an Apple hardware test with from the CD's that came with your machine, see if it picks up any hardware issues.

Is it a 15" or 17" MBP? with dedicated graphics? I ask because a friend of mine has one and had gfxcardstatus installed and had it selected to integrated only, so stuff became really laggy, he was about to take it back to the apple store but I noticed it

 

Few other things you can do:
- Make another user on your machine and see if the problem persists when your in the new user.
- check if your dedicated GPU (GT 330M) is actually in use, go to system profiler, then the graphics section and see which GPU has a screen attached. Or install gfxcardstatus, which can tell you in the menu bar.
- A restart. Sounds lame, but they can work wonders sometimes
- Definitely a Hardware test to make sure the problem is or is not hardware related

A thought I am having right now is that maybe the GPU isnt being clocked up to the standard 500MHz (when the GPU performance is needed) from the low power mode (around 120Mhz). Dont know how you can check this though unless your in Bootcamp.

 

Okay, so I was having this exact problem with SCII, the fix is easy, but check some other things first.

Make sure you turn off the graphics switching and keep it on discrete graphics (the dedicated card).

Make sure that your fans are running properly - playing the game you should be around 4-6k rpm.

Go to your SCII folder and somewhere in there is a repair tool -- run it.

And lastly, (this is what worked for me) here's how to reset the SMC. If you have a battery that cannot be easily removed (all newer model MBP), then follow these steps.

1. Plug in your computer.
2. Shut down your computer.
3. On your built-in keyboard, press and release (left side) shift+control+option+power button (it shouldn't look like it did anything)
4. Now just press the power button to turn it on.

Done. If you do have an easily removable battery, then google smc reset and it has instructions on apple's support site.

You also might want to reset the PRAM.

Hope that helps!