I've tried ReactOS and I wasn't impressed, probably because it's still in alpha. it doesn't really do much you can't do with Wine, and my philosophy is that you're better off dualbooting than mucking about with compatibility layers or emulators.
Wine right now supports a suprising amount of Windows software, and IMO the project as a whole is excellent. People who dismiss Wine as crap are idiots, IMO, as Wine has successfully managed to reimplement a huge chunk of the notoriously awful and non-orthogonal Win32 API. The problem is that the Win32 API is fundamentally broken to begin with, which is why the Wine project often breaks some apps when they "fix" others. Over time though, it has progressively gotten better IMO, and I'm using it to some extent already. I do not yet reccommend Wine for most end users, as it isn't yet mature enough in terms of installation and ease of use, but in terms of application compatibility, I would say that to a large extent, it has "arrived." Emulators also have their place. My business websites run OpenBSD on VMWare Server, installed on a physical Linux server that I rent (for $99 a month plus mucho bandwidth).
Note also that ReactOS is *not* an emulator to any extent. It takes the Wine APIs and provides an NT-like kernel and base system. It's an interesting and exciting project in a number of respects, and I for one am enthralled by the idea of a Windows-binary compatible NT architecture OS that is not controlled by Microsoft (and subject to MS-style stupidity). The ReactOS project, Wine and Samba are three of my favorite open source projects, as they collectively attempt to turn MS's dominance on its head (and are technically impressive).
Plan 9 looks interesting, but it's not aimed at desktop use as far as I know.
Plan 9 and Inferno are my favorite OSes, but they really are more abstract art than operating systems. That said, Plan 9 was originally developed for decentralized networks...it can be used as a "terminal" install, or as a "CPU server" install. The tragedy with Plan 9 is that historically, it failed to catch on due to an almost complete lack of marketing, and the fact that everyone was already either standardized on UNIX, or standardizing on Microsoft. Plan 9 lately though has seen a resurgence of interest, thanks to IBM installing it on one of their supercomputers, but whether or not Plan 9 and Inferno technology is actually usefully deployed to any large extent remains to be seen. As OSes go though, in and of themselves, they are by far the best, IMO.
used to be under OS/2 Warp,
was cool in it's time, not so much now
Its still fun to play with. The lack of applications always has been the main problem, but at least you can run Firefox and Thunderbird on it for full Internet access. Also, on a modern LCD (which OS/2 will support fully) with 1280 x 1024, going full screen in Win16 (read Win 3.1) mode is pure awesome.
Solaris X
Solaris supports only a narrow range of hardware, and the low level user might be frustrated by it, to a large extent.
Theo de Raadt is kind of an ass, and Eric S. Raymond is always willing to aggravate the situation.
Theo de Raadt does rub a lot of people the wrong way, but he's in charge of just one project, OpenBSD. There are also FreeBSD and NetBSD, and various members of those projects who have some degree of a sense of rivalry towards Linux. Its worth noting that there remains absolutely fierce rivalry between NetBSD and OpenBSD; for a time, OpenBSD-associated IP addresses were banned from the NetBSD server IIRC.
Note also that, to my knowledge, and that of several others, Eric S. Raymond has never ripped on the BSD community, at all. ESR actually stands in the middle ground between BSD and Linux, preferring BSD licensing but using Linux on his desktops. His loyalty is to the more abstract concept of the "Unix-nature", which both Linux and the BSDs posess. For that matter, I can't think of any prominent "Linux" developers who have ripped on the BSD community to any extent; while the reverse is unfortunately common, most Linux guys simply don't seem to care much about the BSDs, one way or the other.
There just really isn't a heck of a lot of difference between BSD and Linux, from a technical perspective. Nor, for that matter, is there much difference between Linux and Solaris.