I created this thread to focus on how to keep things private on iPad. I'll add some of the info I know about, and maybe others can add what they know. Starting with basics:
You can passcode protect your iPad access in Settings > General > Passcode Lock.
If you want to keep others from making changes to email accounts, buying apps, seeing or buying certain content (such as music with explicit lyrics), and more, you'll find that under Settings > General > Restrictions.
If you want to browse privately in Safari, go to Settings > Safari and you can select private browsing; toggle on and off for cookies; select auto-fill for passwords; block popups and more. Note that Privacy Browsing will interfere with auto-logons and block some video links, even if they're perfectly harmless, like some videos posted on this forum.
Other browsers, such as Atomic, have private browsing settings as well.
There are privacy apps available for free and for sale in the app store.
Two apps I've messed around with are Photo Privacy (free, with high ratings) and My Secret Folder (99 cents, with high ratings). Both let you set passwords. Photo Privacy lets you store photos, of course. My Secret Folder lets you store photos, notes, Web bookmarks and such. My Secret Folder also offers a setting to take a photo of anyone who tries to access that app without the right passcode. Of course, iPad 1 has no camera, so that feature won't work on that device. My Secret Folder's icon appears on your iPad as a folder named My Folder; changing its name isn't an option right now.
This kind of privacy might come in handy for various uses, even if you have nothing risque on your iPad. For instance, if you share your iPad with others, you might want to keep people from accidentally deleting or otherwise messing up your content. You could also keep your own folder for Web links that you don't want scrambled with other users' favorites. In my case, I have images, legal docs and notes from work that could use extra protection.