My longtime colleague and programming guru Kean Walmsley wrote a great blog post talking about why AutoCAD R13 was painful, but it had to happen to re-architect the product.
A brief history of rearchitecting AutoCAD (or the importance of R13)
I was a customer of R13 and suffered on the heels of a rock solid AutoCAD R12 until the patch R13c4a was released. R13c4a was what the initial release should have been. I joined the company January 1998 when we were releasing R14.01 codenamed Pinetop which was rock solid. Everyone and almost everything experiences growing pains at some point.