Truthfully? It's a techie toy that I like playing with. I'm enthralled with the idea of doing so much with what is, essentially, a disposable device. Not that I'm throwing mine away, but I'm willing to risk things with it that I wouldn't consider doing to a more expensive gizmo.
The big draw of the NST for me is the outdoor-readable screen. I'm relegating it to the role of my "beach computer", something I can grab and take along easily, yet get a few important things done when needed. Those are:
1. Reading. I use the stock B&N app, as I find it just fine for basic .epub files. I use the B&N Library for organizing files.
2. Email. I'm using maildroid for corporate (Exchange), gmail and IMAP access (total, 4 accounts). I don't use the Gmail app at all. On demand to save battery.
3. Calendar viewing. Calendar pad lets me see any calendars I sync to Google Calendar. Unfortunately, I can't find a 2.1 Eclair-compatible program that will integrate my Exchange calendar and contacts. Enhanced Email is ideal, but only runs on 2.2+.
4. Tasks. I use Astrid tasks. On demand to save battery.
5. Subscriptions. In addition to a few B&N magazine subscriptions, I have Calibre set up on my home system to download content for a number of newspapers and magazines each night. Those are dumped into a Dropbox folder that I sync to my NST on demand using Dropsync. They all show up in the B&N Library under "Newsstand", complete with pretty covers.
6. Notes. I use Evernote to sync between my other devices. Given the small keyboard on the NST, I'll probably mostly use this to view notes, though I can punch them in on the NST in a pinch.
7. Newsfeed aggregation. I like My6Sense.
8. Casual (infrequent) web browing. Opera Mobile works, but it's no joy to use given the device limitations. Still, in a pinch, it works pretty well.
9. Voicemail. I read my voicemails transcribed by Google Voice. I suppose I could send SMS text messages, but I haven't done much with this. On demand to save battery.
10. Weather. On demand to save battery. I use WeatherBug.
11. Password safe. I use Keepass, synchronized with other devices via Dropsync.
I've also found it handily replaces that stack of magazines on the coffee table, so I keep it laying around the family room when not otherwise in use.