I’ve come to believe that the number of the Service Pack for any Microsoft product actually is code for how they feel about the release.

• Initial Release = “Hey this doesn’t crash for most people! Good luck getting any work done with it though!”
• SP1 = “Ok, all the really broken crap is fixed. But it’s still now how it should be”
• SP2 = “This is about as good as it’ll get. You can probably depend on it now”
• SP3 = “You really should upgrade to our latest product, but here’s an update in case you don’t want to pay us”
• SP4 = “Dude, this product is totally dead. Why are you even still using it?”

For different products, there might be a +/- factor of 1 SP release or so.
I’d point out that Apple loves to do the same thing. Someone should chart the MacOS 10.x.y releases in the same way. It seems like y is consistently greater than 5 before the series is retired.
The open source world is a little different. There, nothing ever reaches 1.0.
This post was inspired by the performance suckage that is Outlook 2007. I finally joined the downgrading bandwagon.