I am less interested about BB+DRBD+RHLinux combination for implementing system monitoring clustering. Instead, I am more interested about Hobbit+Solaris 10+Sun Cluster software. Sorry to hijack your subject into mine.

Sun Cluster software is now free for use( see R1)

R1: http://www.sun.com/software/cluster/

I use hearthbeat (for all our linux cluster) and suncluster (for 2 solaris cluster). I don't have a big knowledge of SunCluster but it seems to me really more complicated. From what I remember you also need a fc disk or some scsi disk connected to the 2 machine to work as quorum device for the cluster and it's a bit intrusive inside the OS kernel with his drivers (I don't know if with solaris 10 and new version of suncluster something has changed).

I know it's more sophisticated but also really more complicated and difficult to setup related to heartbeat and it's free to download and use but I don't know how much support you'll get for the free version if you have a problem.

Hearthbeat setup will take about 5 minutes and all you have to do is to edit 2 file ... And it also run on Solaris (I didn't test it but at least it's what's written on the website :D)

Francesco