Whether TRIM is useful or not depends on the controller and firmware used in the SSD. In a good SSD implementation (Intel's, and probably a few others), the drive can use “unused” blocks as scratch areas to help even out the performance and ‘wear’ of the device. When a drive is fresh from the factory, it starts out with every block in an “unused” state. As the OS writes data to it though, the drive has to mark blocks as “used”, even if the OS went back and ‘deleted’ the files that use those blocks.
What is TRIM
The SSD itself (usually) has no idea what kind filesystem the OS is using on top of it, so it has no way of tracking which blocks are actually used by files versus which block were previously used by files that have been deleted. This is because as far as the drive is concerned, a file deletion is nothing more than a write to certain blocks hold the information about the directory in which the deleted files resides (a normal file delete operation does not touch the file data itself, which is why undelete utilities have a chance to restore deleted files).
The TRIM command (when it is supported by both the SSD and the OS) will allow the OS to tell the device which previously used blocks are now available for the SSD to use. It allows the OS to ‘trim’ the SSD's concept of what is used down to what is actually used by the filesystem instead of the SSD's conservative concept of “anything that has ever been touched is still (potentially) in use”.
OK for an OS?
While TRIM support could help an SSD maintain optimal performance, it would not seem to me to be a critical factor in deciding whether to use it as an OS disk. Few drives and only the most recent OSes actually support TRIM, yet that does not stop some people from whole-heartedly recommending SSDs for the OS and applications (at least the top-of-the-line ones, not so sure about your Kingston one).
TRIM support via Firmware Update
Whether your device gets TRIM support is really up to your vendor. You will have to take it up with them. I suspect that the better devices will be upgradable with TRIM support, but certainly not all existing devices will end up with TRIM support.
Go read AnandTech's SSD reviews for lots of good information: