You can mess up your tablet "IF" you do some wrong steps. Wish to list terse ( one line ) bullets to make it direct. There are other post that lay out the details.
The forum has a VERY nice search function. It is silly not to take advantage of it.
1) Do not put cm7.2 'internal' upgrade on the 8GB units ! Fixed ! ! ! !
2) Do not load Chainfire3D drivers on your cm7.2 . . . . . this one killed me !
3) Using cm7.2 'external' on 8GB and 16GB units will not touch the nook's original os.
4) Using the 'Ubuntu - total wipe & re-flash' will erase your 'serial number' and 'deviceID'. Fixed ! !
5) Recoveries can and will FAIL if you have a damaged partition table.
6) Some sd card's brands ( Lexar ) and classes ( 10 ) will work poorly ( or not at all ! ) in your nook as your external os.
7) Always flash on a full battery.
8) Always format your sd card ( first ) with fat32. . . . . ( sdformatter v3.0 )
9) Side loading will not work until you turn 'on' unknown sources in settings \ applications.
10) Display is easily the #1 battery drain... Want it to last longer, dim the display.
11) Loading in 100+ apps will only take away one third of your ( app ) storage. . . . . typically, your mileage may vary
12) Your nook will not charge if turned 'on' and using your phone's charger.
13) Key app in GingerBread / cm7.2 - app2sd is not available / usable in ICS / cm9.
14) OTA stands for 'Over The Air' - B&N is sending your ( stock ) unit an update.
15) The devs need to fix tough problems, so please don't post in their area.
16) Rooting your stock NT does NOT block OTA's.
17) Take note of apps with "HD" in their title. They require h/w accelleration ( which we do not have working yet )
18) If its 'off' but the back lite is still 'on' then it is hung.
19) One possible way to get it out of a hang is to: press and hold the 'N' button and the 'Volume Up'. Now in addition, press and hold the power for a count of ten and let go.
20) Always backup before trying something ( anything ! )
21) Turn 'off' unknown sources when you don't need it. New virus uses unknown sources to infect your tablet.
22) CM9 is in 'alpha' for 16 and 8GB units. Please don't load unless you understand the risk and know how to back it out.
23) Ad-hoc tethering works ! Must apply a wpa_supplicant fix via adb to your rooted nook
24) Use a partition manager to resize your booting sd and regain the unused space on the card. ALERT ! Danger ahead !
25) Windoze 7 people have to remember to 'right click' and then 'run as administrator' .
26) cm9 will quit working on purpose. http://forum.xda-developers.com/show...&postcount=446
27) the b&n usb cable is "special" and plugs "deeper", which is required for charging.
28) the microphone is NOT working for a lot of people with cm7 & cm9. devs will fix... soon...
29) if your stock nook says software version 1.0.0 ... it is not OTA blocked. ... Heads up !
30) Connecting useful items to usb is called "usb hosting", which is NOT working yet.
31) Never trust a big download. ( especially if its slow ) Use md5 crc checksum to validate the integrity.
32) You can clean up your 'Dalvik cache' in Titanium Backup, goto menu / more.
33) if you're ONLY interest is reading books then the 'rooted' stock 'os' is best. do not install cm7 / cm9 ( yet ! )
34) when given the choice between App Installer, and Packaging Installer, always choose the second.
35) for cm7, an error has been reported in the build.prop file that results in emmc not mounting when connected to a PC
36) want to see what's going on with your memory/partitions ? get 'free' app "Storage Analyzer" to see internal and external !
37) asked to make a logcat/dmesg report ? get/use free app, 'Voodoo Report'. you can reboot and mail it to yourself.
38) turbo prop tweak : http://forum.xda-developers.com/show....php?t=1684997