I got flack for my e-mails always showing what device I was on, like I was showing off. Now, my Blackberry and my iPad both read, "Sent from my Atari" when I send an e-mail. It makes a great conversation piece!
One of the first things I got rid of. I like the iPad but don't see any good reason why I should advertise for Apple. Nor does anybody who gets an email from me need to know what whizbang superkewl goodie I sent it on.
i think that people using the native apple signature just want to show that they have the device. one of the first things i do when i get a new i device i remove the signature.
It depends on which email account I'm using. On my personal I left it on there as is, on my business email, I moved it and am using my own. Of course I leave it on all forum posts because after all, iPad is the BOMB!