Well ,it has been about 2 years or so since i own a N900 but trust me i love it since the day i bought it and my love has not been any less till to date .A greatest machine ever .I am not going to tell you all great things that maemo5 contains as you know them already .
Even that N900 was launched in 2009 and this is 2012 today where there have been so many new devices launching every other day but to me ,really ,nothing can be compared to N900 .
I am a medical student so probably i dont have much time to deal with all the things my N900 has inside it but what about you ?
things which i still i am working on to understand or to learn ..I know there can million things but i am just going to point out some big fishes here .Its not that i cant understand them ,its just that my N900 keeps me so busy that i dont find enough time to deal with all the things which it is capable of .Only some of them are :
( 1 ) i have not understood queen beacon widget (qbw completely though i know some about it .
( 2 ) smscon editor is the 2nd one which i have not tested fully as i know there are plenty of features there ,though i know some of them but still there are things to test or to know .
( 3 ) Emulators such as mine craft which run high quality games ,i still have not touched them ,not yet ,so i wonder how amazing that would be .And i still have not been able to run all the games that N900 can run flawlessly.
( 4 ) i have not installed meego software on my n900 not yet ,neither i have tested ubuntu .i could manage to install nitdroid 2.3.4 ,still got to do something about 2.3.7 upgrade .
( 5 ) i still have not learned how to increase rootfs or how to increase space for more apps through a partition .

Well sure there are other plenty of things which are still being hidden from me as i chose maemo ,so every day is like a new day for me .And yeah there have been many other apps such as host mode beta , bless N900 ,blue-tooth tethering,cleven, MMS etc ,actually there are loads of them .
So i have my reasons to still keep my N900 for about 10 years or so ,or till N900 says goodbye to me forever . Between what are your reasons ?
DO share them ,through this we may able to find new things about N900.For example i just noticed last day that there was a panorama app for N900 which was banned from nokia later on but still i managed to install it on N900 and guess what it looks real great ,indeed .
Feel free to let us know what you stiill have not learned about N900 ,it might offer help to understand or to find new things about N900 . Between i have not fly a drone with N900 as well ;p .Adios .