You know I take it in stride that Apple will have to fix something whenever the new OS ships because they spit one out every 18 to 24 months and (although it was a secret) has been developing for intel and power pc chips in a parallel manner and the worst problems are usually quirky and only impact a few users.
What I don't get is that Microsoft takes years to develop each new OS and what they release usually ought to be called a beta because its so buggy. XP was utter trash when it was released, it took Service Pack 2 to get it stable and reliable. Millenium Edition had so many problems they went to XP rather than mess with it. Win 95 was as buggy as the landfill in summer. Win 98 was probably the most stable release off the shelf they've ever made.
I live in a dual Win/OSX world and use both daily. I wouldn't be terribly worried about buying OSX 10.5 when it releases in the Spring, the only hesitancy I would have would be whether the PPC version is fully optimized when shipped because of the push for the intel machines. But there is no way I'd ever consider buying a new Win version until the first update ships because of the quality control issues.
If I were advising anyone buying computers right now I'd tell them to buy something with XP installed or I'd tell them to wait until after the first Vista update.
I love my Mac but they are terrible in their support for enterprise customers and because they don't do a great job of discounting for big purchasers it'd be hard to suggest to a business needing very many machines.
As I've said before, if I were starting a business I'd probably go with a linux based set-up because of cost