I'm still a bit confused. The 1.x to 2.x transition was intended to be a breaking change (hence the major version bump). I don't see how you had application issues during that, as 1.x and 2.x were parallel-installable, and apps had to make a conscious decision to upgrade.
I don't recall the stability of the 2.0.x series, though: it's possible they didn't get things right and were still making breaking changes even though it was the stable series. I don't remember that being a problem, but I'll admit my memory of that period isn't perfect.
I do remember some app developers prematurely upgrading and releasing versions that depended on early development releases of 2.0 (and later, on the 2.1.x unstable series), which often did cause breakages. But that was really the app developer's fault for depending on versions that made no API/ABI guarantees.
Sorry, I don't recall the particulars since it was a long time ago. But believe me, there were lots of problems with the libraries. I still cringe whenever I have to deal with a Gtk library.
I don't recall the stability of the 2.0.x series, though: it's possible they didn't get things right and were still making breaking changes even though it was the stable series. I don't remember that being a problem, but I'll admit my memory of that period isn't perfect.
I do remember some app developers prematurely upgrading and releasing versions that depended on early development releases of 2.0 (and later, on the 2.1.x unstable series), which often did cause breakages. But that was really the app developer's fault for depending on versions that made no API/ABI guarantees.