I rooted mine last night. The process is probably difficult for someone who doesn't have much command line experience or experience with the android dev tools, especially adb. You also need to delete the default windows drivers and install a custom driver. Post install requires some very specific and deliberate action too. Not exactly one-click root.
Once rooted there's a package that installs the market and other tools. I havent been able to install busybox so I can't install vnc server or any app that depends on busybox.
There are some large issues here though. It does not have hardware buttons like back, home, etc. No back and menu button means you can't use apps correctly. Someone at XDA wrote a softbuttons program but it is of limited utility. The softbuttons pop up over the menu when you click the menu button, which is incredibly annoying. It might be better to remap the volume keys as back and menu. I'm assuming thats possible.
I use adb to install apk files and use the market (once installed). Some apps just crash on loading (youtube and others). Some works just fine. So far I have angry birds, an app for work, a couple synthesizers, weatherbug, and some utilities.
The lack of hardware buttons is incredibly frustrating. As well as the issue that your market purchases don't appear in your nook's launcher until you reboot entirely. The device, I'm sorry to say, runs slow in general. Its noticeable in apps that really utilize the CPU. I like the rooted nook, its like an ipad jr, but its really in rough shape. It sounds like BN is going to be hostile to installing apk files or joining the market, but if their own market has enough stuff they'll probably keep people very happy.
That said, the stock nook is actually pretty cool. I turn comic books files into PDFs and read them with the native PDF reader, which is excellent. I have all my BN purchases. I have epub files from 3rd party sources. The web browser is really good. Its pretty much a typical 2.1 browser. Pages can be slow to load, but not unusually slow. I love the 7" size. I see people all the time with ipads holding them awkwardly like a baby. My nook fits in small bags, large pockets, etc. I dont even have a case for it. I have a screen protector and nothing else.