I paid a visit to the parts MB parts counter yesterday (first time I might add!). Anyway, I learned some useful information about the MB key cylinder. As mentioned earlier in this thread, it costs $96 (vs about $35 for an aftermarket). But there are some benefits.

1. Its made custom by MB for your car based on the original key that the car was built with. They also cut a new key to test out the cylinder that they make for you. And they toss in that new key for free.
2. If your key for an aftermarket cylinder is lost, MB will not be able to do anything for you. (search 'drilling out key cylinder'). However if you lose your key for a MB cylinder, its a simple matter of having a new key made.
3. Your current keys will work in the new MB cylinder and of course, the new key will open all of your current locks (door, glove box, trunk).

I guess this means that if you buy an aftermarket cylinder, have a BUNCH of extra keys made with the $61 you saved over the MB cylinder. And your pocket/purse will weigh a tiny bit more with the extra key you'll need to carry around.