The Android OS is completely open source. You can take and build your own, functional, android OS to run on any device you damn well please. NITDroid is a perfect example of this.

However, you will not get certain closed source packages such as Maps, Market, Gmail, etc. Those are google's proprietary software that they sell as the "google experience" with certain manufacturers and their phones. If you actually pay attention the google's Cease and Desist they did not say cyanogen cannot provide ROM's to the public - he cannot provide roms with their proprietary software to the public (specifically: he released their shiny new market before they did and pissed them off). Now I personally disagree with google's take on this, especially with their "Do no Harm" motto, but they did have the right to do so.

You cannot take Maemo sources and build your own Maemo OS on any device you damn well please. There is closed source components to the basic Maemo functionality that prevent you from building from scratch and even getting to a usable desktop.

In this aspect: Android is more open than Maemo. With Android you can build and create your own, functional OS, from sources. Even Stskeeps, the creator of Mer, agrees with me that the core of the Maemo OS is not entirely OSS and it causes a LOT of headache for him in building Mer.

However: The only official devices with android on them are locked out and prevent root. Google spends a lot of time locking up and fixing bugs that caused people able to root their android devices to take control. On the other hand, Nokia doesn't give two shits if you grab the rootsh package from the Extras repository and do whatever the hell you want with your device.

In this aspect: Maemo has a more open environment than Android, as the oversearing company is more open to allowing people to have access to the device they purchased.

@DaveP1 - Android only allows you to gain root if you build your own.. there is no "root me" app in the official Google Market like there is in the (mostly) official Maemo Extras repository. So Both Android and Maemo aren't on the same field as far as "gaining root" and tinkering with it.