I used to enable TRIM using 3rd party software, and I had to do it all the time Apple released a minor upgrade. Recently I installed OS X 10.8.3 on a SSD and when I was ready to install the SSD in a new MBP, 10.8.4 came out. I installed the SSD in the laptop and upgraded to 10.8.4. To my surprise TRIM was enabled.
Anybody else with the same experience? My SSD is a 512 GB Samsung.