|www.rodneybeede.com||"I would love to change the world, but they won't give me the source code" - unknown|
Useful guide that I used on Fedora 17 with success.
It may lower your security since free space can now be determined as such (TRIM may cause empty cells to appear). Your data is still encrypted, but an attacker could look at the contents now and know which parts have data and which don't to make attacks more feasible. Just depends on how much encryption you need and whether it is okay for an attacker to be able to guess the size of data.
You will get the potential benefit of better write performance and longer life on your SSD.