Because I am a sys admin that needs the ability to connect to my servers and network gear via ssh, connect to a help desk via the web, connect to my network management software from the web and monitor my Nagios set up to see server status on a few hundred servers in near real time.

The N900 is the only piece of hardware that lets me do all that with something I can carry in my pocket.

Just wish the email had a few more bells and whistles like different alert tones for different accounts and more than one exchange account support. Then I could dump my blackberry and be happy