The arguments being made for the N900/Maemo are very poor in my opinion. I don't think anyone is going to be able to name a feature that is needed in a mobile device that the iPhone lacks that the N900 possess.
iPhone 4S (jailbroken) - No contents winner. It can do every single [practical] thing an N900 can do, only much faster and in a much more practical fashion. There is no debate.
Social networking/social media, navigation, translation, dictionary, voice control, graphic and movie editing (on the device), educational and mathematical tools, internet browsing (there is Chrome on iOS now), etc.
I can't control my regular TV using IR, however I can control my Google TV with the Google TV app. but lets be practical, who ever really used the N900's IR?
The N900 is a hackers/tinkers delight, however I challenge anyone to make the argument that it is more practical than an iPhone 4S. I have owned an N900 for a very long time and I love the N900, but there is no debate to be had - it can do anything the N900 can do, only around five times as fast and more efficiently.