why does my macbook get so hot so fast?

Open Activity Monitor in the Utilities folder. Select All Processes from the Processes dropdown menu. Click twice on the CPU% column header to display in descending order. If you find a process using a large amount of CPU time, then select the process and click on the Quit icon in the toolbar. Click on the Force Quit button to kill the process. See if that helps. Be sure to note the name of the runaway process so you can track down the cause of the problem.

And, you need to provide more information such as "how hot," as in providing temperatures and what you are doing.

Macbook Pro is a notebook and not a laptop - User Tip: How to deal with MacBook Pro and MacBook heat?

Per your user manual: Do not operate your MacBook Pro on a pillow or other soft material, as the material can block the airflow vents. Never place anything over the keyboard when operating your MacBook Pro. Never push objects into the ventilation openings.

From MacBook Pro: Care, Use, and Safety Information

For prolonged use, place your MacBook Pro on a flat, stable surface. Do not place your MacBook Pro on your lap or other body surface for extended periods of time. Prolonged body contact can cause discomfort and potentially a burn.

Mine had this same issue, when I checked Activity Monitor it showed that Samsung Kies Air Agent was using %87 CPU. I uninstalled and haven't had an issue since.

Same issue, turned out to be Kies also... 127% on KiesWifiAgent!!! Honestly what the heck is it doing. Killed it and now things are back to normal.

How can the %CPU be over 100? And my QuickNote app was using 99-101% CPU power! I had not even touched it in a few days!

How can the %CPU be over 100?

If you have multiple processors (ie dual core / quad core CPU etc).

The usage of each CPU is measured in percent, and the usage of all the cores is summed to give the total. The total usage of two processors can be up to 200%, the total for four up to 400% etc.

Thanx Kappy,

In my case it was the Quick Look Helper.

I'm on the MBP 17" with Snow Leopard.

Had to Force Shut it.

Worked well.

Thanks, Spotlight was using 99%. MBP 13" retina