Is it safe to disable FileVault?

I'd back everything up first, obviously. As long a you have enough disk space to do it, it should work fine. Just make sure it won't get interrupted somehow...

As long as you have enough free space on the HD disabling FileVault should be quite safe. With "enough space" I mean at least as much free space as your home folder occupies, preferably a bit more. (A tip is to move stuff from your home folder out on "shared" areas, and restarting, before disabling FileVault.)

I "got back" a couple og GB when I did this a while back.

I still wouldn't do anything this big without backing up all the data I couldn't afford loosing.

I used Filevault for about a week. It messes with a lot of processor-intensive actions, like importing raw video or audio. Never had any file problems turning it on or off, just took a long time, so it should be fine.

i didn't know people actually used it...

I don't trust it. I don't think it's quite ready for practical use. I've heard far too many people losing their data because of FileVault.

YOU would have.