The kernel used with Linux Mint 11 has a power regression in the code, that causes it to not be as conservative with power use as previous kernel versions. This warning is in the release notes. For Linux Mint 11 they are at http://www.linuxmint.com/rel_katya.php
, and it also directs you to read the Ubuntu 11.04 release notes (as it is based on that). From https://wiki.ubuntu.com/NattyNarwhal/ReleaseNotes#Linux_kernel
you can see to expect 10% to 30% increase in power consumption in laptops (and thus reduced battery life and increased heat).
This is well known and heavily documented and investigated at Phoronix. There is a patch available however, for kernel 3.2, and it will likely be included default in the next kernel. Details: http://www.phoronix.com/scan.php?page=article&item=linux_aspm_solution&num=1
. Linux Mint however uses the 2.6.38 kernel versions, so that doesn't help you. Switching to Linux Mint 12 and manually patching your kernel might be an option (you will have to compile your kernel).
Another alternative is to force your CPU to use a lower operating frequency. This will save power (and heat, and battery life) also. Add the CPU Frequency Monitor (or something like that) to the panel (right-click it, select add to panel) and you can set the frequency or power conservation method there. You need to add one for each core on your CPU BTW.