Tag-Lines in a Democratic Internet

 Talking about marketing and brand identity, the debate of these days has been the following:  what is the role of tag-lines in web 2.0.  The issue is more than philosophical -- it is ontological... If we accept the concept that web 2.0 designates a participative community, where users define the tone, the content and the nature of the community, then we should reject the idea of having a tag-line to drive the community towards any preconceived end. This is the underlying idea of an authentic democratic community, where labels and tag-lines are disturbing the purity of the natural identity. Indeed, the community identity is never defined and continuously evolving, wherever the users are willing to take it.
Twitter does not have a tagline, nor does Digg, Blogger, Technorati, Craigslist (if you consider it a web 2.0) et many others.
On the other hand, some web 2.0 services have built their identities leveraging tag-lines and often changing many overtime.
Facebook is a good example - here is its tag-line history:
“Keep up with friends and family,” “Share photos and videos,” “Control privacy online,” and “Reconnect with old classmates.” Now Facebook has a simple message to entice you to sign up: “Facebook helps you connect and share with the people in your life.”
Is Facebook managing its tag-line reactively or proactively? In other words, is Facebook reacting to the users' behavior, so to hone the potential of its brand - or - on the contrary,  has Facebook elected to pursue a specific marketing strategy, irrespective to its users?
I understand that, once you have reached the dimension of Facebook, such question become a chicken and egg question...  However, I am keen to believe that the importance of auto-determination of an online community is expected to impact the use of tag-lines (or - at least - the evolution of the same).
Some other examples - Youtube "Broadcast Yourself", and Myspace "a place for friends".
Now, empirical evidence shows that only a minor percentage of Youtube users is actually uploading videos representing themselves, while the majority of the users is just "watching-someone-else."  Most of the users would rather mirror themselves in a tag-line such as: "find-here-the-TVshows-of-the-80s-you-used-to-love-so-much,"  or also "show-your-friend-a funny-video"...  Of course, these are not quite the actual lines to have under a logo... but I mean the content-message of these tag-lines is closer to the community than "broadcast yourself", even though I concede this last one sounds very nice...
Now, I believe you are ready to try this exercise on your own, with Myspace "a place for friends". (Friends? Sure...)
If you are curious to read more tag-lines click here.