TRIM is only officially supported by Apple for the SSDs that they install on their Mac line.  If you install your own SSD you can still enable TRIM with Terminal and some commands or use a program called TRIM Enabler. I used beta 4 version of the program on my Intel X25-M G2 160GB SSD and it worked perfectly. The author just released version 2.0. Below is a short write up from Anandtech.

TRIM Enabler article from Anandtech.com