Quick answer, probably not. With the newer versions of Windows (2000, XP, and Vista) I see no real reason to go out of my way to upgrade for a business. Primary reasons for this:
1. The software applications we use are critical and we do not have the time to fiddle with them. Examples are Visual Studio and Adobe Creative suite.
2. These same products are very expensive to upgrade.
3. My business is working already.
Even though we try to set standards here, we have had employees download the Betas, and there are issues. Too many to handle during business hours.
Even when the team has tried simple upgrades like Internet Explorer 7, we run into isses with personal on the design team seeing different things. This is unacceptable in our environment.
And to tell you the truth, we could be running Windows 2000 and not seeing the difference right now.
I'm sure new pc's will come with Vista when released, and that will be fine as long as our core software works with it.