I think one of the best examples is the "dashboard" application switching and the use of the terminal. Even in Android, switching between programs and closing active processes is a little more "hidden" from the general user. With Maemo, i hit the dashboard and I close a running application and I know it is closed. Yes, there are running processes in the background, but I can be more engaged in knowing what those are.

The fact that the terminal is an application readily available in the stock version of Maemo is another example. I can get a terminal in a moment's notice, and with a little work (not a lot) I can have root access and have a bash shell and use traditional linux commands to manage files. In iOS this is nonexistent and in Android it is a bigger trick to pull off.

Also in Maemo, you do not have the hardware trying to keep you from changing it. In certain builds of Android, the unit will try to reset certain settings to the carrier approved settings. There are certain apps you are not permitted to remove or add. All of these are simply there to stifle the user's freedom and to generate revenue for the carrier.

I think its funny that you describe the N900 as a computer with phone function, because it does a better job of being a phone than the iPhone 4!
I have wavered in my enthusiasm for Maemo and meego (I was recently using the HTC Vision Z/ G2, man thats some slick Android!), but I cannot deny that it is an advantage to have a phone that is unequivocally mine and not artificially limited by the manufacturer or carrier.