How soon is "very soon"? Gnome 2.6 is still quite young. 2.4 was out for quite some time before 2.6 saw the light of day. I think there's still some serious development to be put towards another stable release (or at least I'd assume so).
10.4 is also due "soon". Aiming at OSX is like trying to hit a moving target. Apple are ahead of the OS design game, and have been for some time. Microsoft are finding it a struggle to implement features for 2006 that Apple succeeded with 24 months ago. I think it would be naive of the GNOME devs to try to be a "10.3 ripoff" when 10.4 is just around the corner.
That said, GNOME used to be my least-favourite WM slash Desktop Environment for Linux (When GNOME was still 1.2, KDE2 was so much more polished), and has quickly become one of my favourites in the last 12 months. The GNOME devs deserve credit for how quickly they've improved their product lately. Just looking at home many applications come pre-GTK'ed these days is enough to convince me that others feel the same.
Architecture and OSes aside, it's great to see developers improving the desktop metaphor. WindowsXP is nothing more than Windows95 with prettier icons, and I'm glad both Apple and the Linux community are trying a few more daring ideas these days.