Does FileVault 2 interfere with TRIM when using an SSD?
I guess I wasn't that convinced, so I tested this empirically. 

Setup: MacBookPro6,2, Mac OS X 10.8.2, FileVault2 enabled, Crucial C300 256GB (firmware 0007)


With TRIM disabled, I nearly filled the disk (5 GB left) over the course of everyday usage. Deleting ~50 GB of files, I then tried to create a 50 GB disk image. Results were pretty pathetic - an initial peak at 180 MBps quickly dropping down to average writes of about 15 MBps, the disk clearly stuttering (showing periods of zero writes where presumably the disk was trying to catch up). The file was deleted, and afterwards I enabled TRIM. Again, I tried to create the disk image, and again I got the same results. Finally, after deleting the disk image, I created a disk image for the third time - with freshly TRIM'd bits. Average performance was 200 MBps and was sustained.

So no, FileVault2 does not interfere with TRIM. (And no, garbage collection is not sufficient, Crucial.)