The New York Times has a really interesting article ``They criticized Vista. And they should know.'' (you might need to register to see the article, I am not sure). It shows why Vista isn't really an upgrade to XP, mostly through emails between senior Microsoft executives. Basically, they knew it was a dud, and instead of going with the more honest approach they were at first planning, went with really misleading advertizing that made things much worse.
There probably are many good things about Vista under the hood. But the two most visible ones (the pretty interface and the interconnectivity) are such a problem that users hate it. [The interface is a pain on older machines, drivers seem to be a problem all across the board].
I certainly see similarities with certain Maple upgrades (documented at length already on primes) as well as the recent fiasco with the <maple> tag and the lack of notification emails here on primes. As far as shipping an overly buggy Maple, as far as I know the reason is the same as Microsoft's: both companies needed a new product out in the field to keep $$$ flowing in.