A Q&A posted on Nokia Connects answers a lot of interesting questions about the Nokia Lumia lineup. The Nokia Lumia 900, for example, will launch with improvements to the camera and sound systems, which will trickle down to the Lumia 800.
Nokia claim they've optimized focus and color balance on the Nokia Lumia 900 compared to what we saw on the 800, but since the two use the same camera module, the improvements will be made available to the Lumia 800 as well. They will possibly be a part of the major camera update that brings the native panorama app.
The Nokia WP7 top dog also features improved audio as a result of hardware and software changes. The software side of things will be made available to the Lumia 800 too.
There were plenty of questions about connectivity - tethering, for example, will be available on the Lumia 610 and 900 at launch and come as an update to the 710 and 800.
The Lumia phones don't have penta-band 3G (like Nokia's Symbian, uh, "Nokia OS" phones). An AT&T Lumia 900 will work in Europe though.
The dual HSPA+ on the Lumia 900 shouldn't affect the battery life as the 900's battery is "optimised for HSPA+ and LTE" whatever that means.
One thing the Lumia 900 has that its smaller sibling, the 800, won't get is GLONASS support, which often improves accuracy of the positioning services.
Nokia are aware of some of the limited customization options of the Windows Phone platform and are working with Microsoft to fix them.
no plans for supporting Lumia phones in the Nokia Suite software, however, Zune works just fine they say.
You can read the full Q&A for some more info about the Lumia 900 here.