coming from a legacy 5000+ seats microsoft installation we evaluated linux vs. opensolaris. decision has yet to be made but opensolaris has come out very attractive, not least because of the security model and integration with id-management products sun offers.
we would get support for os, openoffice and mysql from one vendor. being able to run linux software with little to no modification is also a big plus. we liked zfs for our storage-requirements but there are some headaches with older storage solutions we still have to keep around.
what sucks is the lack of drivers for commodity hardware, missing package system and open office still has ways to go to be as easy to use as office.
I hope sun manages to ride out the current slump. looking at the way both markets and regulation (!) is heading they really do offer a very consistent software & support strategy, they are just a little to much ahead of time...
hp-ux indeed is a joke for the majority of markets. proprietary software and hardware lock-in - that is so 1992! and then the regulation nightmare when you deal with public clients on a large scale.
and one more word on niagara - if you look at the berkeley paper you'll see that in this application the cell beats the niagara by 2x, but then it runs at 3.2ghz versus 1.4ghz on the niagara. I really start to wonder what a 2.1ghz niagara would do.
btw - ours run at 1.2ghz and we are perfectly happy with the performance.