I have since two days ago near my G1 and Milestone also now a Nokia N900. I have therefore now compared with each other and this will now reflect my experience here.

Pro N900/Maemo:

• Maemo is more open than Android root access on terms again. Say rootsh (root local) and OpenSSH root (via SSH connection) are installed directly on the Programmmananger, and you have root access, either locally in the X-Terminal and / or through an SSH connection.
• There is an unofficial Android 2.0.1 port for N900 (see maemo.org Forum). But that does not matter here, yes.
• The applications on Maemo run as a native ARM binaries. This means that the N900 visually at least for me seems a lot smoother than my Motorola Milestone with Dalvik-VM, which has exactly the same CPU with the same clock and same graphics unit as the N900. Say both have a QMAP3430 SoC with the same clock and PowerVR SGX 530 graphics than unity.
• 3D applications such as games (OpenGL ES ...

I have for my new G1 / HTC Dream wrote a small tool that retrofitted a missing feature of Android, and the manual re-reading of the (micro) SD card for new media files such as music, video and image files so that they according to an ADB push operation, a afile transfer, a Bluetooth file transfer, etc. without reboot or unmount / remount the (micro) SD card will appear in the Android Gallery. Here is the Download Market QR code for the bar code scanner or link for the Android: