I used my iPad on the ABD trip last week. I didn't have to take it out of my carryon. It worked perfectly for watching a movie, checking email on the plane, reading a book. I loved it for traveling.
I think it depends on the airport. The first few times I flew with my iPad they didn't ask me to take it out. The next few times they told me to take it out and made me go through the security line again. I bought a soft-sided small laptop bag to keep it in when I'm traveling. That way I just pull out the padded sleeve and put in on the container to go through the scanner alone, just as I do with my laptop. I'd plan to go ahead and take it out because some TSA agents will get cranky (as will other passengers) if you hold up the line