where I work we still deploy xpsp2 corporate wide and re-image new leased machines that come pre-installed with vista with an xpsp2 image. Supporting a new os always comes with it's own set of issues and when you have a decent sized user base, it can really cut into preset budget $$$ when you have to move move a large# of IT staff that are developers and put them in tech support mode to assist the helpdesk with dealing with new os issues instead especially when you have alot of IT projects that have established deadlines that won't get finished because you're dealing with the implementation & administration of a new OS corporate wide.
... speaking of waiting till vista sp2, if you wait that long, shouldn't you technically wait for the next windows os at that point. At service pack 2 stage isn't the os considered old at that point? XP is currently at SP2 and I've heard that sp3 isn't even on the release horizon yet.
Microsoft is shortening it's maintenance cycles with regards to os service packs.
- Windows NT Server/Workstation 4.0 last service pack was sp6a (sp7 was mentioned but never released)
- Windows 2000 Server/Pro last service pack was sp4 (sp5 was mentioned & even quoted on a few MS websites but all that was released was an update rollup package)
- Win95/98 rec'd something like a service pack 1 (too small to really consider it a service pack),
- Win98SE same thing I think but I can't remember for sure
- WinXP Home/Pro is up to Service Pack 2 with SP3 possibly coming out next year (don't quote me on that), after which you will not see any further service packs for this OS
- Vista will only get as far 2 service packs and will be replaced by a newer OS afterwards.
I currently have machines with both XP & Vista but if I have to tell the truth, I probably prefer using my xp machines, that may change by next year but that is still a ways away