I think people have, but I have not personally.
I live in Washington state, and everyone knows, it rains a lot in Washington. However...the thing about Washington rain is that it rains frequently, but not a lot per shower. That said, I haven't had this problem (knock on wood).
About a month ago, I went to the dealer with a laundry list of things to look at before my odometer turned the 50k mark. One of the things was the drain tubes. Interestingly, the dealer guy said he couldn't look at it unless the customer states that it has occured or that it's an "issue." I just looked at him and said "so, if I were to walk out that door and come back in and say 'hey, my sunroof leaked I'm concerned with it' then you'd look at it and blow out the drains?" He sort of looked at me, nodded (understandingly) and added it to the work-order.
So...if you are still under warranty you can certainly get it done. If you're not, there is a thread on here (I'm pretty sure) that details how to do it. There was also one detailing how to snip the bottom of the tubes to prevent future back-up. It may've been on another board though too...not sure. May've been the disco3.uk board or whatever it is.
Good luck!