Maybe it's just me, but I've been noticing an increase in people holding hands as I walk along campus lately.
When it comes to dating couples and public displays of affection (PDA), hand holding seems to me a great balance for affirming (to others) that mutual feeling of belonging. Necking and other excessive hugs and kisses can do the same, but in a much more uncomfortable and sometimes inappropriate way for those around you. Now I've said it before that it's only awkward if you make it awkward, but using your partner as a massage chair is not really the best way to show your affection while in public. Similar to a Facebook Relationship Status, holding hands in public is also a more subtle way of deeming a relationship "official". It tells those who know you "I'm with this person".
My favourite thing about the concept of hand holding is that it is a great balance for affirming (to each other) that mutual feeling of belonging. Extending your hand to someone and having them offer theirs in return is an honest thrill; it speaks to our desire for placing ourselves in a place of acceptance by another person whilst risking your own vulnerability. It's not the same thing as when a boy puts his arm around his girlfriend's shoulder or places his hand on her thigh, so as to say "she is mine, she belongs to me". Rather, holding hands seems to signify "we are equals, we are in this together".
Holding hands is in itself a means of communication, reciprocating your affection for each other.
I'd be curious to know what some historical and cultural meanings about hand holding might be.