My two cents...
-- Is 64bit Linux/Ubuntu a worthwhile alternative to use as a general use OS?
It depends on your needs and the level of interopibility you expect. You'll run into the same issues on 64-bit Linux that you'll run into on 64-bit Windows--the same issues that have plagued all processor transitions: hardware support, assumptions about the size of 'int,' etc. Unless you plan on specifically taking advantage of your 64-bit processor, stick with 32-bit. The transition is a bit easier in Linux, as 64-bit varieties have been available for quite some time, e.g. Alpha and Sparc (sort of). Very few Windows applications, server products included, are written to take advantage of a 64-bit architecture.
-- Does Linux make a good secondary OS? (any dual-boot issues, for instance?)
Assuming it's set up correctly, you won't have any issues at all.
-- What is the future of Microsoft's Windows operating system?
Windows will continue to dominate the market for the foreseeable future. Not everyone realizes this, but Windows wasn't Microsoft's first choice in operating system advancement; however, Windows 3.0 outsold OS/2 millions to one, and the market itself made the decision to stick with Windows a simple one.
-- Will Vista be dominant, or crash and burn against competitors Linux/Mac?
In the consumer desktop space, Linux isn't a serious competitor. OS X is fun, but you have to drink Apple's Kool-Aid to play. Apple's laptop market share is steadily increasing, but I think Boot Camp, Parallels, and now VMware have had a lot to do with that. I love my MacBook Pro, but I run Windows more often than I run OS X.
-- Will Windows XP do for another 5 years?
Microsoft will continue to support Windows XP until the next major release of Windows, i.e. the one after Vista. They may, however, choose to cheat and pull another Windows Server 2003 R2 type release (in which support for Windows 2000 was discontinued). As has been noted, sales of Windows XP will end sooner rather than later, but it's support that's the primary concern. As long as there are enough Windows XP users in the marketplace, and there will be for quite some time, hardware and software vendors will continue to support Windows XP as well.
-- Is Leopard gonna kick their buts out the desktop market?
Apple's computer products are still a niche market, regardless of what Apple would have us believe. It's a good thing the iPod rules the portable music player market. Without it, there'd be no Apple.
-- How big is the desktop Linux userbase anyway? What gaps in the market has Linux filled?
I think the numbers are exagerated, as they tend to be based on downloads of distributions and not an actual installed base. Linux is the swiss army knife of operating systems. It does many, many things very well, but very few distributions do those things out of the box. Expect perceived desktop performance to continue to decline as more and more focus shifts towards the server market.
-- How commercial is Linux?
In the server market, very commercial. Novell and Red Hat are doing quite well selling support contracts. In the desktop market, not so much.
-- Is Amiga coming back to take them all out Lol
You're right, that question was a laugh. ;-)
EDIT
Speaking to the technical aspects of Windows and Linux, it's a toss. Most of the stability issues in Windows are the result of poorly written third-party device drivers. And like anything else, operating systems are only as good as the person using them.
Most of us here really enjoy playing with different operating systems; however, I run Windows 99% of the time. If I need to do *nixy stuff, I use Cygwin or Microsoft's Windows Services for UNIX. That way, I can still play Bioshock--kick ass game, by the way--or do whatever else I want to do that requires Windows.
Trev
