BTW a nice userspace program for the (ext4) FITRIM ioctl() command
can be found here: http://www.spinics.net/lists/xfs/msg01837.html
It's called fstrim and works nicely on my Vertex SSD.
Compile and run as root (e.g.): fstrim -v /
(There is no visible feedback, you have to wait a few minutes
(depending on the size and state of the SSD) before it finishes.)