I've got one!
I am still waiting for my X, due early April, but I do have one in my Accord Coupe. The FM modulator does work however I find 90% of the time I use the speaker in the unit which is loud enough and I don't have to press the button on the unit and the radio to tune in the frequency for the modulator.
The unit is great for charging the phone and for listening. Talking is another story. There is a built in microphone but I find I have to talk at it and loudly for people to hear me. It does come with an external microphone that you can place at a better location which would work well.
As I do not use my phone often I am happy with it.
If I used it a lot I would wire in the external microphone.
It's nice to have hands free, charging and the ability to pop the phone off and put it in my pocket. The FM modulator part works well and for an extra 10-15 bucks it is worth it IMHO.
I soon as I get my X I will let everone know how it works in the X.