I'd probably use it for a lot of work-related stuff (checking email through Exchange, maybe connecting via VPN and ssh'ing into my server boxes, etc.) I'd also use it quite a bit for surfing the internets, playing Linux games, probably play around with VoIP, and also play around with the social media features on the device as well.

But really, I'm really looking forward to using it as a mobile Linux computer; I'll probably end up doing everything I'm using my computer for right now and just do the same thing on the N900.