I am using the N900 mainly as an extended media center in addition to my other devices.

My Samsung Galaxy Nexus 16 GB is my prime phone and is additionally used for Sygic GPS, camera/video + camera apps, E-mail/Social Media and some browsing and news apps.

My Blackberry Playbook 64GB is mainly used for watching movies, reading comics and E-mail/Inet browsing + office work (writing notes etc.) and phote editing.

My N900 with 48GB is stuffed with music (in combination with a Mini Boombox), is used as a USB drive and USB host, is my prime night camera (bless), back-up normal camera, use of the various camera apps, holiday hotspot for my Playbook and back-up Sygic GPS.

It is a nice companion and I found a good goal for the N900, but I cannot use it anymore as my main device. As back-up and as addition it is great though.