There are many lists out there on why to get Vista, so here's mine on why not to.
1. You don't actually need it -- No, think about this. Vista doesn't do anything you can't already do with XP. About the only significant shift requiring Vista is DirextX10, but as no titles support it yet and, according to John Carmack (the godfather of modern gaming) there's no need to yet either.
2. Cost $$ -- It's so blindingly obvious, most people will be blinded to it. You already have XP, and alternatives like Linux are free. If you really want to throw money away, go give it to a local charity.
3. On that note, it's outrageously overpriced -- at least in Australia. As revealed in the current APC, even after taking into account the profit margin Microsoft Australia previously applied to XP (as well as exchange rates, as you would expect), Australians are paying hundreds of dollars more for their copies than in the US. In fact, it's cheaper for Australians to buy Vista direct by mail order from the States. If you think Microsoft Australia is reaming us, vote with your wallet.
4. Upgrading hardware -- XP was demanding at release, but Vista more so. If you have an older machine that struggles with XP at the best of times, Vista is out of your ballpark unless you spend even more money to upgrade. If this is you, see point 1.
5. Driver support -- Key hardware like video and sound is crippled at the moment -- while Nvidia is working furiously to get a stable driver for the 8800 out by the 30th, there's still no SLI support for any of the Nvidia range. And thanks to the removal of hardware accelerated 3D sound in Vista, Creative's popular DirectSound based EAX no longer works at all, muting this feature for just about all gaming titles on the market today. Creative is in the process of coding a layer for its drivers to translate EAX calls to the OpenAL API which is seperate from Vista, but going by past experience with Creative drivers we won't see these any time soon.
6. Applications that don't work -- there's been plenty of coverage about applications that won't work without a vendor update. These include anti-virus, backup and security software such as those from Symantec, Sophos and ilk; CD and DVD burning tools like the suite from Nero need updated versions to work; and even basic disk management and partitioning tools such as Paragon's Hard Disk Manager are awaiting an update for Vista to be compatible. How many more will fail as Vista enters mainstream? Even Firefox has issues with Vista.
7. It's a big fat target -- with a new and untested in the global wild architecture, virus and malware authors are going to work overtime exploiting the holes Microsoft missed. In fact it's already happening. Loath though I am to use the word 'security' and 'Windows' in the same sentence, Windows XP has at least been patched to the hilt and can be used with a plethora of reasonably effective security tools that work now, without waiting for an update down the track.
8. UAC -- Oh yes, the Microsoft solution for an operating system where mutli-user was an afterthought. Sure, you can disable it, but the OS then makes it clear then that the onus is on the user for any damaging programs that got to run with permissions, rather than with Windows in the first place. If you do have it on, it is going to annoy the hell out of you. It pops up far too frequently, and even on a fast PC, the UAC screen takes too long to come up and disappear.
9. DRM -- And to a lesser degree TPM -- were made for the RIAAs and MPAAs of this world, and the even tighter integration of copy protection mechanisms and 'Windows Rights Management' into vista are nothing more than a liability to you, the user. This ComputerWorld piece says is succinctly: 'it's hard to sing the praises of technology designed to make life harder for its users.' As for TPM, this short animated video shows just how far the rabbit hole goes. And to think you pay for the privilege of having the use of media you purchased and own dictated by third parties, even on your own system.
10. The draconian license -- somehow, Microsoft has forgotten that it built its business from products that empowered its customers, not hampered them. Of course, we forget that Microsoft's customers aren't you and I, afterall (see point 9). Aside from the backward thinking that is licensing, and not actually owning, your software new terms with Vista include being able to transfer the license only once; half the limit compared to XP for Home Basic and Premium on how many machines can connect to yours for sharing, printing and accessing the Internet; limits on the number of devices that can use Vista's Media Center features; activation and validation governing your ability to upgrade hardware and use Windows itself; and outlawing the use of Home Basic and Premium with virtualisation software, and Ultimate only if DRM enabled content and applications aren't used. But then again, who reads these anyway?