(quick post 'cause I'm at work. more later.)
AFAIK, Nokia *tried* to push their gtk+ patches upstream, but upstream wasn't interested because they change some really core gtk+ stuff. Essentially Nokia's gtk+ is a minor, incompatible fork for all intents and purposes. I have a feeling you'll find this situation in a lot of other parts of the system as well. We really did try to use Ubuntu packages, except where using an Ubuntu package would cause us to have reduced compatibility with Maemo 5 software. Even with those guidelines, Mer has hundreds of packages. Please, look at the Mer project. Look at our repositories, and our OBS page (the builder we used).

-John