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Aluminum gets hot quickly, but it doesn't mean that your MacBook is hot inside. However, if you want to make sure that temperatures are correct, use Temperature Monitor > http://www.macupdate.com/app/mac/12381/temperature-monitor In a normal use, your computer shouldn't have temperatures higher than 80ºC.
Note that fans will be turned on automatically when your computer needs, so don't worry about it
The MacBook Pro will get warm with usage, the metal case is part of the heat sink system that the computer uses in addition to the cooling fans. The side with the processor will heat up first since that is the greatest source of heat. If you feel that the MBP is getting too hot, or too hot to handle, take it back to an Apple store genius bar and have the technicians test it to be sure all is normal.
the use you place on it will also affect how fast and how much it heats up...things like gaming place a burden on the system and produce a lot of heat.