If you don't want receive ADs for your KSO, you can...
I got KSO few days ago from a friend, i don't expect the Kindle3 special offer version, frankly, the ADs don't very much bother me.
however, when i reviewed the forums and found still there're quite some people are looking the way to disable the ADs, and I also did some tests and found it is actually very easy
YOU DON"T HAVE TO JAILBREAK
1. connect your KSO to computer
2. enter system folder on kindle (you may have to show all hidden folders and files)
3. there's a folder .assets (if you have already received ADs)
4. delete this folder or rename it (you may have to use command interface)
5. create a blank file name .assets (in windows command window, you can type copy con .assets, then press f6)
6. you don't even have to restart, but i will suggest you do so
7. ADs will not be downloaded anymore even if you connect to wifi
however, the screensave will always prompt you to download ADs. and banners too. i actually prefer it shows ADs
and i think if you have jailbreaked it (when it is FW3.2), you may now use screensaver hack to change to your own screensavers. however, my kindle is upgraded to 3.2.1 and as i understand it cannot be jailbreaked now. so i cannot do further test.
if you decided never go wifi again, you can choose not to create the .assets file, then the normal screen saver will be show. however, if you connect wifi the AD will also come.