I'm going to preface this by saying that I know nothing specific about tribalism in Libya, so this is all going to be on a more general level since I do know something about tribes more generally (though it's hardly one of the areas I'm most comfortable with).
This post is basically a reaction to Friedman's post from the 22nd.* The issue of tribalism is an important one for discussing how these revolutions might possibly turn out in the Arab world, tribalism is certainly a major barrier to successful democratization and strong tribal structures can certainly go a long way towards short circuiting democratic transition.
However, this is true of just about any powerful ascriptive identity that is present in a population. Too often talk of tribalism is used as some kind of excuse for why we're so advanced and the rest of the world is so far behind (Friedman's column doesn't quite step into this, I have some other issues with it rooted in IR theory, especially about artificial borders since virtually all borders are artificial, but they're not worth taking up here. I could also go on for awhile about the tribe's with flags bit, it's more complex than that, but not worth it).
But tribal identity isn't that much different from the kind of personal and local loyalties that were present throughout Europe before the rise of the modern state. They're not that much different from powerful lineage groups that were present at points in Chinese history. Comparing and contrasting these forms of identity would probably take a (series) book, so I won't go in depth here.
My point is that while ascriptive identities such as tribal identities certainly are a barrier to democracy and something that needs to be considered when intervening, it's also something that was present at some point in all successful democratizers since it is a universal trait. These forms of identity were usually overcome at some point well before democratic transition, especially in the west where wars against the cities, landowners, and religious wars, all served to help reduce personal loyalties and replace them with loyalty to the state, but history shows they can be overcome and often have (sometimes with explicit recognition of the divisions such as in Lebanon) even later in the process of development.
A common theme in replacing these earlier identities with something more akin to national identities is violence. It is not necessary, but a frequent way of developing a national myth is a revolution, such as the American or French revolutions (though in both of these strong earlier identities had been substantially eroded before revolutions, in the American case mostly due to emigration to the colonies).
The relevance of this to Libya is two things. First, tribal identities are a reason for caution, but they shouldn't be given too much importance. These forms of identity are not constants, they change as institutions change and its fully plausible they haven't survived the heavy urbanization of Libya in strong enough form to be an insuperable barrier. While tribalism was a problem in Iraq, Libya doesn't seem to have the further complication of sectarianism. The second point is that the resistance to Qaddafi provides the germ from which a more modern form of identity can emerge that suits a modern state (not necessarily western nationalism, but tribal identities aren't very compatible with the kind of hierarchical authority pattern based on the rule of law essential to the functioning of a modern state). This was lacking in Iraq and is a major problem in that country's ongoing attempt at transition (among many others).
An excellent article on Libya's tribalism also a appeared in the NY Times on March 21.
*I'm finally getting around to this after a busy week trying to get some work done before vacation in San Diego, which I've finally arrived in and will be here till Monday. Starting next week posting should become more regular again.