Even locked iPads can be jacked with some button-pressing and a smart cover, according to 9to5Mac.com.
Bad guys won't gain complete access to a user's tablet, but anything that was locked is fair game. So if the tablet goes to sleep and you were in email, or contacts or settings or anything else, the world can get at it. Or at least the person holding an iPad that isn't theirs.
9to5Mac has a solution, too: disable Smart Cover unlocking in Settings under the General tab.
Here's their vid: