I've had a NC for about 2 weeks and been running the Honeycomb 3.0 (preview 4) ROM on it from an SD card. At first I just tried out Honeycomb to see what it was like. I didn't expect to run it as my daily NC OS.
The preview release of Honeycomb definitely has some issues on the NC. It's not likely to get any better until Google releases the source code for Honeycomb and devs can work from the official source. No one knows when this will happen, but probably within a few weeks to a month.
For what I use my NC for Honeycomb is fine.
Web browsing:
The browser is really nice. I like the tabs, the way it handles bookmarks and the thumb menu navigation (you turn it on in the options and if you touch the side of the screen a menu appears, very handy for 1 handed use).
Occasionally after running the browser for a while I'll notice pages will stop loading and things will hang. If I go into the settings > applications > all and force close the browser everything is fine again. Sometimes I can go days with out the issue sometimes it happens after a few hours.
Tabs are nice. However switching between tabs and closing a tab can be VERY finicky on this build. You have to touch it just right.
The majority of my NC tablet use is browsing the web.
Apps/Games
I only use a few apps and games. I moved them over from my Evo and installed them on my NC. (I haven't bothered rooting and/or installing the market and Google Apps yet, waiting for final).
USA Today (phone version)
CNet
Engadget
Angry Birds (barely play but did test it out and it worked)
Pocket Legends (works great, I play it frequently)
Winamp (works well, the lay out stretches funny but usable)
Kindle (works great)
Adobe PDF (I've read large books on it with out any issues)
Aldiko (seems to be fine, read books on it as well)
XDA app doesn't work, crashes on launch.
The gallery app on this ROM is broken so you can't view images. It was like that on the SDK image this ROM was built from so no way to fix it. I installed QuickPic (an alternate gallery) to get around the issue.
I've noticed a little LAG on this ROM, but not too terrible.
One other small goofy issue is that if the NC sleeps long enough the Wifi will disconnect. It's not a big deal though, but sometimes when you go past the lock screen you have to wait 10 to 20 seconds for the network to reconnect. It's a minor annoyance though (and I think you can work around it with a screen unlocker)
While Honeycomb meets my personal needs (even with the issues in this build) it may not be for everyone). With it likely being a month (at the soonest) to a little longer before the source is released and a better ROM appears. I've considered switching to the Froyo ROM. So far this ROM is doing everything I need though, which is why I haven't switched.
I hope that helps. I'll be happy to try anything out on the NC for you and/or answer any questions I can.