There are two differences, one general, one specific to sandforce-based drives, although I will explain them below pretty much purely for interest. As a punch-line most users shouldn't worry about it, and most will not notice at all.

1) For all SSDs, Bitlocker will do a one-time pass of filling the empty drive with encrypted "junk" so that it's not clear what's in use vs. not in use. Because this makes the entire drive seem "full" to the SSD controller, there can be some slowdown. It is generally not enough to worry about for general use -- it's still a lot faster than a hard drive, and AFAICT it still plays nicely with TRIM, etc -- but it may be worth leaving some unpartitioned space to increase the spare area if write performance is at a premium (eg, if you have a 480gb drive -- which comes out as about 450 usable in Windows, thanks to drive-manufacturers using 10**9 for a gigabyte, and Windows and everyone else using 2**30 -- maybe partition 425 rather than the full 450.

2) For drives with a Sandforce controller, the use of Bitlocker means you will get no benefit from the built-in compression. They're still pretty fast, and you're unlikely to notice the difference with the better models (using sync or toggle flash), but once again if write performance is at a premium, this can be an issue (and the cheapest models with async flash are definitely best avoided with this one.)

In terms of buying drives for it, I'd still go on reliability first, but that might swing the recommendation to Samsung over the Intel 520s given that the latter have a Sandforce controller. We've deployed a ton of laptops with the Intel 520s (and before that OCZ Vertex 3 and Deneva 2, also Sandforce-based) and bitlocker, and I've never heard of a reaction other than "wow, this is really fast" (often even compared to an older-generation Intel or Toshiba SSD, rather than just against disk.)

There's also one other point I should make: almost nobody will do this frequently enough to care, but because there are a few crazy people out there... blowing away your system and doing a fresh install with bitlocker -- or switching between encrypted and unencrypted repeatedly -- will overwrite the entire drive every time. Done once, twice, a handful of times isn't going to matter in the slightest, but done repeatedly over long periods of time this is one of the few "abusive workloads" which could prematurely wear out the drive.

I mention the above given a thread I saw elsewhere suggesting that someone should encrypt their drive before every time they went outside the US, and then decrypted it when they came back. Don't do that with an SSD, at least if you're going out of the US regularly.

Also as an aside regarding Bitlocker -- it has a bigger CPU performance hit on older CPUs -- Sandy-Bridge and newer machines (eg anything in the X220/T420/W520 generation or newer), barring some some lower-end CPUs have the "AES-NI" feature which makes the computational cost of the encryption almost free.