I've been tinkering with Subsites on SS 2.4 rc1 after trying it on 2.3.7 for a bit and while the install for 2.4 went flawlessly, the admin interface doesn't seem to be switching between different sites in the top-nav dropdown. This is keeping me from being able to test this potentially ideal solution for a client.
I don't usually tread this bleeding-edge with client sites, but you folks seem to be doing a great job of moving things along.
So - can a guy get a check-in on what exactly "not supported" means and if this module is languishing or if there are people banging on it alongside the eminent 2.4 release?
Much much much thanks from a hack who's dabbled in several different CMSs.
Make sure you are running the latest versions of both 2.4 and subsites trunk (since they would be in parallel development). If you run into bugs check the open tickets on http://open.silverstripe.org for the reported issue.