As a counter-point, did you know that more service packs have been released with bugs, than cumulative updates? I can recall a grand total of 2 CUs that shipped with any problems whatsoever, and at least 4, maybe 5 service packs that shipped with major issues, a couple of them show-stoppers. All this while there are up to 17 or 18 CUs released to every service pack. The major problem is that, in spite of what they promised back in 2005, just about every service pack has had fixes *and* features, while CUs avoid this to a very large extent. Like Microsoft, I also spend a lot more time testing a service pack than a CU, because in comparison, so much has changed.

Not saying that a sloppy CU isn't possible in the future, but to date, the track record speaks for itself.