It's been only two weeks since Maverick Meerkat was released and already the flood gates are opened for Natty. If you check out the development section of the Ubuntu Forums you'll notice the activity is already well underway. The early adopters really enjoy the punishment.
There's really not much going on in terms of actual development (as in coding) since the developers are preparing to discuss the blueprints for Natty at UDS. So mainly it's just automated syncs with Debian as is usual at the beginning of each Ubuntu development cycle. Also, there's toolchain preparation work which usually means updates to compilers and various core system libraries.
It seems over the years the Ubuntu development process evolved so that the three releases immediately after a LTS focuses (mostly) on foundation work. Those puzzle pieces then get their final spit and polish in the next LTS.