I purchased my iPad direct from Apple. This included a free option to engrave two lines of text on the back. I've got my name on the first line; house number and UK Post Code on the second line.
If I lose my iPad, time is of essence. That's why I want my phone and email immediately visible. Someone can quickly call, text or email me, before I leave wherever I lost it, for instance.
If I lose my iPad on a trip, at the airport, etc., I want it right back. I don't want to wait till someone can write me a letter or hopefully drop it off at my house and such. My aim is to make it as easy as possible for someone to return it to me, quickly.
That's also why I don't count on battery life or tech savvy, and have a sticker on back as well with contact info, along with my onscreen info.