With the imminent release of OpenSolaris, we have the prospect of one or more OpenSolaris-based distributions such as SchilliX as an alternative to Solaris proper.
Would I use such a distribution? Almost certainly not. Not that I have anything against an OpenSolaris-based distribution, but my primary interest in OpenSolaris is that it's the base for Solaris proper. As such, the "distribution" I'm most likely to run is something along the lines of Solaris Express.
So if I'm happy with Solaris Express, what benefit do I get from OpenSolaris? Well, quite a lot actually.
Simply being able to look at the source is an invaluable aid to understanding the behaviour of the system and debugging problems as they arise. Looking at the source, it can be immediately obvious what the problem is. (Or, equally, that the problem isn't where you first thought so you can eliminate that line of enquiry.) Something that has often frustrated me in the past is that I've often been able to make a fairly confident guess as to the nature of a problem, but haven't been able to confirm it. With source code, I can trivially check; without, I have to wonder whether to fight through the process of a service call. (Note that Sun should also benefit from its customers being able to do problem diagnosis themselves.)
As a true open source project, you won't need a service contract or have to log a support call to report a bug. If something isn't right, you'll be able to report it without any hassle. This is something I've wanted - even as a contract customer - for years. The overhead of raising a support call is sufficient that many smaller problems I spot would go unreported. And the overall quality of Solaris will only be improved if bugs get logged. So making it easier to report bugs should lead to a general increase in the quality of Solaris.
Beyond the ability to report a bug or ask for an enhancement is the opportunity to fix the problem myself. Either for my own personal use, or to be put back into the main product. I'm not going to be writing kernel modules or filesystems or device drivers, but there are plenty of irritations in the standard commands that could be addressed.
My primary interest in all this is Solaris. Sun have decided that OpenSolaris is the development mechanism for Solaris going forward. As such, getting involved in OpenSolaris is a natural thing for me to do. Other distributions look to be a lot of fun, but (by their very nature as being a distinct distribution) aren't going to do the same things that Solaris proper does. So while I'm going to watch them with interest, I'm going to be actually running Solaris or Solaris Express.