Yep... we use it. Just started a few months ago.
There was a bunch of hollering about it, but it's not so bad. You get a little (ish) key-fob-like-thing that you have to press the button, it displays a 6 character key that you have to type in next to your login name and password. The key-fob-like-thingy is a random number generator that works off a pre-set key, so the random generated "passwords" are in a set order, and the MLS you're logging into knows what your key is, so it knows what the random "password" should be.
What this does is only the person with the "key-fob-like-thingy" in hand can get into the system. (of course once in a while I'll have to call the person with the "key-fob-like-thingy" and ask them for a password so I can get into the system from a remote site.
This pretty much eliminates password sharing, which had become an epidemic around here. We had one person in an office signing up for the MLS and everyone in the office using it. We also had friends and relatives of Realtors using the MLS system... which is a very bad thing. Too much critical data like when people are home, when they are on vacation, gate and security systems codes are in the private remarks which only Realtors are supposed to see.
So all in all... it has been nothing more then 6 more characters to type in when logging into the MLS, and it provides a much more secure system.
I say all membership sites like this will be using them in the not too distant future.