Yes it is and the UAE authorities are taking it pretty seriously these days. If you look at recent press reports, they've shut down several facebook and twitter accounts because of such things. If people are threatening you or your family, you can report them to the authoirities and charges can be brought against them.
Here you go:
http://www.7daysindubai.com/UAE-cops-sh ... story.htmlPlus given that a certain forumer has been posting personal deets from people's FB accounts on the forum, she could well come a cropper of this!