I've used it for a while to get high-availability from two NFS servers and I always recommend it in my scalability talk. It's awesome. (Heartbeat which is the "fail-over" software in the typical configuration isn't so great, more on that another time).
Anyway, being at the MySQL conference the context of course is "how can this be used for MySQL". Usually I prefer a simpler master-master replication setup for redundancy. Later in the afternoon Mats Kindahl (one of the replication developers) pointed out how the drbd setup is great for having a highly-available master in a more typical master-slave(*N) setup.
It's funny, just as I write this Paul Tuckfield from YouTube is giving a keynote and telling about the complicated stuff they were doing to deal with failure of their master in their replication system. :-)
If they used drbd the redundant masters would "share the disks" (but you have the content duplicated so there isn't even a disk SPOF). When the primary master fails, the second one would just start up and all the replication slaves wouldn't know the difference. Magic!