Haven't really used it for anything "cool", except web browsing, Gmail, and gaming. But mostly gaming. Games I'm playing: Bakery Story, Gem Miner 2, Sims Freeplay, Grow, N64 Emulator (Mario Kart 64!!), Solitaire, The Island: Castaway, The World of Magic, Warspear Online, FPSe (PSX emulator). Well... I do have my PS3 controllers for the gaming so I guess that's kinda cool.
We use the Nexus 7 for in-flight navigation and to display moving map sectional charts using the Garmin Pilot and Naviator apps.
We've even got it set up to Bluetooth with our Garmin GDL-39, which displays traffic and weather in flight. Very cool!
This all works great, and will be even better when the app programmers set the software to recognize the Nexus 7 as a tablet. Right now these programs recognize the N7 as an Android phone, which disables some of the cool split-screen features.
The cool thing im doing with my Nexus is putting on my new Portenzo case, so glad it isnt naked anymore. The case is awesome. I`ve also been using Perfect Viewer to read comics and Aldiko to read The Hunger Games. Ive also been using EZ PDF Reader to do annotaions on some work documents. I`m an iOS guy but the more I use this thing the more im falling in love with my Nexus.
I am glad I'm not the only one using it for ebooks. I have a kindle, which I actually love using, but its just so easy to use the N7 esp with great apps like moon+ reader and aldiko. My poor kindle feels old fashioned now lol
I've also just discovered Scanner Radio app, it's strangely addictive, try it!
Probably not cool to most people but I've been trying to run gcc, already got python + gae working, other than I've been reading lots of books, this n7 does so much cool stuff I couldn't imagine going back to a device like a kindle that just does one thing.