Mac OS X does not support to trim sector ranges like Windows 7 or Linux does. But with an Ubuntu Live CD (USB Stick) you can even trim an HSF+ formatted file system without deleting it first:

1. Backup your system (Macintosh HD)
2. Burn an Ubuntu 10.10 Live CD (or create an USB Stick)
3. Boot Ubuntu
4. Open Terminal
5. Do the following steps:

sudo bash
add-apt-repository "deb http://archive.ubuntu.com/ubuntu maverick universe"
apt-get update
apt-get install gawk
apt-get install sleuthkit
wget http://sourceforge.net/projects/hdparm/files/hdparm/hdparm-9.36.tar.gz
tar -xvf hdparm-9.36.tar.gz
cd hdparm-9.36
make
make install
cd wiper

6. Run wiper.sh:

// test
./wiper.sh /dev/sda1

// real
./wiper.sh --commit /dev/sda1

(sda1 is the first partition of the first disk, you may need to change this - Disk Utillity will give you the answer)

7. Enjoy the regained speed :-)

Addendum to the SSD Trim Article