to be honest. Surely any responsible software company would issue a Service pack if it found it necessary? We've had this discussion many times, but it's worth having it again, even if we are anticipating events by many months.
Modern software applications, big ones, are highly complex. That complexity brings many benefits from the user's point of view, but it means potential problems for the developer. It simply isn't possible, in a beta-testing environment, to anticipate every set of circmstances in which your product will be expected to perform, and unless you're prepared to spend an unreasonable length of time in beta there comes a point when you must launch to market - and allow your userbase to discover all the tiny little glitches which can surface when someone tries to run 'LeapyDanceyThing' version 2.0.1 in your new code.
Then you can start writing and issuing patches and fixes, and that's what Microsoft does. Unfortunately a company like MS doesn't just have its userbase issues to contend with - there are thousands of people out there who derive satisfaction from searching out loopholes and vulnerabilities in the code, and exploiting them maliciously.
Eventually you'll have enough fixes, patches, drivers, and plugs for holes to make it worthwhile bundling the whole lot up as a Service pack and offering it to your customers as a download. We've seen it happen with Windows 95, 98, ME, NT, XP, and we'll see it happen with Vista.
During its development and beta phases Microsoft tested Vista against almost 2000 widely-used software applications, and probably as many hardware devices, and beta testers (of which I was one) spent months and months testing it against all kinds of different hardware/software configurations; it would be difficult to imagine a more robust testing regime. Now we have a public Release Candidate that was downloadable by anyone on the planet with a broadband connection and a suitably-specced computer. That means the code is now running on millions of computers, and the feedback is flooding into Redmond. Over 4000 Microsoft employees are working flat out on the Vista project, and by the time the code goes to gold status (meaning it's ready to go to production) it will be stable and compatible with as many devices and applications as possible in the circumstances.
if it's necessary to release a Service Pack down the line that shouldn't be a problem - we should welcome it in fact.