I have a few minor notes, though, in response to your notes:
1.) Replacing the motherboard does invalidate the warranty, but other hardware changes, no matter how many, don't...you simply have to call Microsoft.
2.) Honestly if I had to pay the current prices for Windows I wouldn't be running Windows on most of my computers, I'd be running Ubuntu, Knoppix, etc. Thankfully I receive a limited number of free licenses from my employer. (They have an agreement with Microsoft so they buy licenses in bulk and eat up the cost.)
3.) Microsoft now makes you agree to a special disclosure when you install the WGA updates, but I agree that they should have been more up-front from the beginning and that it should not be considered a critical security patch.
4.) Security is definitely a problem. What gets me to some degree, though, is that Symantec, McAfee, and others have complained about Microsoft securing the kernel. I understand that they fear losing control over it, both for financial and security reasons, but while AV software may be locked out so is malware. That's a good thing overall. They've also complained about Microsoft creating the SecurityCenter and also creating OneCare. I wonder how they'd react if Windows suddenly was as secure as Mac OS X.
5.) Yep, Ubuntu certainly does run faster than XP on my computers.
6.) Actually you'll be able to activate Vista an unlimited number of times, just like XP. The catch is that you'll only be able to activate it on two different computers during the key's life. Microsoft intended to have that limitation in XP but never added the wording so XP can be moved to new hardware an unlimited number of times.
7.) I don't agree there. If you agree to the licensing agreement then you have given them the right to limit your usage of the software, as opposed to not being able to use it at all. However, I do disagree with some of the licensing terms, such as the restriction on moving the license only once as well as the new restriction on using Home Basic and Home premium in virtual machines.
The security, performance, and licensing issues have not become great enough for me to switch to Linux, particularly since I don't have the expense of purchasing licenses, but I do dual-boot some systems with Linux distros and use my Ubuntu LiveCD frequently. We'll see if/how that usage ratio changes in the coming years.