As most modern computers produce a fair bit of heat after extended use it behooves me to point out that laptops in particular have "issues" with being in "sleep mode" for extended periods. Sleep mode happens when you just close the lid without actually powering the system down, this leaves some background tasks running to keep the current user logged in and running programs in memory (that's why the computer pops back on when it's opened and you push the power button), this is fine for a quick trip to another room or such, however when you place it in a carrying case there is no airflow and dangerous levels of heat can occur. I'm sure you'd rather not buy a new computer every 6 months as, like most of us, you're not made of money. So remember if you do not see this when you unpack your computer from it's carrying case,
you're doing it wrong.
I've included a sidebar app Found Here that looks like this, for your convenience.
The red button completely shuts it down, green restarts and yellow locks it (like when you just close the lid). On a side note, if you use your laptop for long periods you might want to invest in a laptop cooling pad. Wal-mart carries several kinds for $15 to $25, just look for one that fits the bottom of your computer.