I use my iPad for so many things it would be impossible to list them all, but using SqueezePad to listen to music, finding places to eat using maps while traveling and having a guaranteed conversation starter would be my top choices.
When I bought it I thought it might be useful - with several hours use (minimum) every day it is indispensable.

[About using the iPad to view slides]

Snicker. That IS funny!

Two uses I did not anticipate:

1) A remote control and Guide browser for DirecTV
2) Hook up bass pedal, headphones, and bass and use Amazing Slow Downer to learn songs on my bass. All without disturbing anyone else. I even rip bass lesson DVDs to my computer and load them on the iPad to listen, watch, and play along.

Bruce

When I got mine, in May 2011, I expected that I was going to play music (etc.) and read books, and generally use it as a travel computer for personal use. The one big use I've come up with that I did't expect was photo support. I've been taking it to my son's sports events, downloading the camera's memory card, editing during downtimes, and emailing shots to other parents as we go along. If I had known that, it would have made a good case for getting the 64 gb version instead of the 32, since pictures by the thousand fill up the memory fairly quickly.

Love the slide viewer idea. thanks. I was looking for that.

I am using it pretty much as expected. However, I recently decided to develop applications for the iPad and iPhone. I didn't expect to do that when I bought my iPad 6 months ago!

That I'm using it for everything.

Games!

Media.

HBO Go + Netflix. I bought it primarily for surfing the web but it quickly became my second television.

Here's a big list. GPS, Maps, Sims, I think you can play Poptropica not sure, and that's basically it, Apple is very smart so I expect A LOT OF THINGS from Apple.