I've had the Nexus 10 a few days now, enough to have used it quite a bit, thought I'd throw together an impressions post. Will break it down by topic.
Form factor - coming from an HP Touchpad it's just so much lighter and easier to hold on to due to the slightly grippy back and the much lighter weight. The screen is pretty spectacular to look at.
OS - I like the split notifications and settings in the top bar, and I like the overall smoothness vs the hacked ICS build that I had running on the Touchpad. No complaints about speed whatsoever.
Web Browser - Came with Chrome installed, I was surprised with the very high screen resolution how rarely I notice aside from text being super smooth. Bill Simmons' Grantland is one exception I can think of, where the text column jumps into a funny place by default.
Video - With such a bright high-resolution widescreen video is a natural thing. Netflix, Hulu+ are both pretty great looking. HBO Go has the best UI I've seen them do anywhere (comparing vs Laptop and Web). XFinityTV has one of the rare scaling problems, where some of the channel logos are teeny tiny inside big buttons. The Youtube app fills the screen well considering the low fidelity video.
Reading - I don't think a backlit tablet will replace the Kindle for me any time soon, especially the new PaperWhite. The Kindle app does look good on this screen though and offers lots of options. I've also been using News360 for both the widget and the app itself, which is quite attractive an offers a wide variety of content. I messed with Pulse also and preferred that one. Also ponied up the $2 for the "golden platinum" edition of the Reddit is Fun app that has added a good tablet UI.
Forums (this place) - Tapatalk is up there with the basic Twitter app in the "waste of real estate" app category, with just one column browsing. I feel like they could imitate the Gmail or Reddit (mentioned earlier) apps and do something with columns in landscape, to jump between forums/topics without hitting back constantly. May email them about this, it's a paid app they should get with it.
Email - I've written a couple of emails in the Gmail app, and I like the columned UI of it. Can't say too much. But that brings me to...
Keyboard - the 4.2 Android Keyboard is kind of lame, no long-hold for symbol support at all, so have to constantly switch modes for numbers and symbols. Lame like the iPhone, where I don't like the keyboard much at all. Ponied up for SwiftKey tablet but it's still pretty awkward in-between thumbable and single-finger tap. Would use an outboard keyboard for any serious typing. (Writing this on my laptop)
Games - Not a huge tablet gamer but I downloaded one of my favorites, Puzzle Quest 2, and it looks good and loads quickly. My one complaint is that a lot of the board game translations are iOS only right now. Hoping Microsoft adds SmartGlass support for tablets, while I don't love the keyboard on this it is preferable to the controller-based on-screen one on the 360.
Social - Not on Facebook or G+, using Plume for Twitter right now though I'm open to suggestions if there is a better tablet-friendly client.
Photography - I really like the interface of Glimmr for browsing my Flickr account. I bought the premium for the higher resolution previews. The camera on board is emergency-only grade, and I don't want to (often) be "that guy" taking photos on a tablet.
2048px.com has some good wallpapers and I found some other "iPad Retina" ones in geometric styles that I like. Really hard to get my own photos to work well as a wallpaper because of portrait/landscape and how it scrolls. I really don't share a taste with whoever does the default Android backgrounds for Google, I think they use some gross palettes.
Other - Maps and BostonBus map look and work great. Bank of America has a good tablet-only version of their app that may be better than their desktop web site. Looked into Google Magazines since I have a couple of paper subscriptions, they don't translate over and it's a total rip off.
That's pretty much what I've played with. Haven't messed with the music apps (pandora/spotify) that I'd use online because I'd tend to use them on headphones or better speakers. Nothing else really sticks out so far.
What are other people using on the Nexus 7/10 or other Android tablets?