Apparently I’m not the only one thinking this way about Vista. Though it looks awful pretty, and if I bought a PC with it installed I’d probably have a hard time convincing myself to buy another XP license just so I didn’t have to use Vista for a few months! On the flip side, I would definitely consider holding off a hardware purchase that included a Vista license for a few more months, knowing a Service Pack is imminent.
Of course, if they’d got it right from the start, I’d be running Vista already… as it stands, I’m not too likely to drop $200 on something that runs slower than XP, supports less hardware, has arguably-worse power management, and makes the occasionally excruciating UI mistake (most notable is the automatic replacement of the “sleep” button with “install updates and shutdown” where updates are available). Really, the main reason I’d switch is to have consistent UI between Office 2007 and the rest of the system (instead of the presently absurd Vista-ish (but not actually Vista) UI available on XP), newer hardware (insofar as XP isn’t available), and a paid-for upgrade path… I’d rather fork out my money now and trust that another 3 service packs are coming, rather than pay full price for an OS and then pay full price again, and again. I acknowledge this is partially a psychological thing stemming from my opposition for paying for point-releases, but even so… many of the alleged ‘upgrades’ in OS X are thoroughly trivial.

I’m surprised I’m still on Vista — I have always upgraded, then downgraded shortly after until a service pack comes out, but with Vista I have noticed significant improvements every Thursday as MS releases their new update packs.
Everything’s running pretty well for me now, and I have Vista on 2 laptops and 1 desktop, plus we’re using it on about 20 computers in the office. A lot of users in the office who have been upgraded to Vista machines are really liking the slight interface changes — they all adjusted very quickly (after my 2 minute tutorial on using the interface), and even the former die-hard Mac users are saying they don’t mind being moved away from OSX now.
I’m sticking with Vista.
Apparently, though, according to someone I was speaking to recently, Vista OEM licenses are fully backwards compatible with XP, so you can install XP using the Vista license key. I haven’t tried it though.