The audio, camera, and power management parts shipped with most OMAP3xxx parts also have completely open specs. Combined with an open driver for the N900, basically all you're missing is the baseband code (which makes it no worse than the Moko in many respects), the SGX driver, the 'energy management' (read: battery charging logic) code, and the bootloader. While it's true that there is no open source SGX driver, there's no real alternative for mobile 3D, so slating device manufacturers for that seems a little unfair.
You'll note that CSD as shipped with the N900 is closed, but ofono is open, and Nokia are heavily involved with the project, aiming to replace CSD with an open alternative, so.
Assuming you don't want 3D, and are prepared to ignore the bootloader (given that it's really just a BIOS that can load a Linux kernel) as you would a BIOS on a PC, then all you're missing is the battery-charging stuff on the N900, at least when ofono arrives. That's not perfect, of course, but still seems pretty damn good to me.