I know for a fact in MD it is LEGAL to use your phone's GPS while driving and so I would assume it would apply to tablet's as well. So worst comes to worst i just pull up the map when I get pulled over haha. I am going to go out on a limb though and say I really don't think their are any laws in MD pertaining to the use of tablet's while driving. The laws they do have are directed towards cell phones and are specific to talking, or texting while driving. Using GPS on phone's is absolutely LEGAL. And as of now the phone law's are a secondary offense, meaning you would have to be doing something else in the first place to get pulled over.
Like I said though, I really don't think there are any tablet specific laws..........and ultimately, I just don't care haha. If for some crazy reason the tablet ever causes me trouble with the law then I might start caring...a little.