Hashtags make sense, if only to encourage folk to focus on a particular topic. So many tweets veer into random thought territory... and oh, what a waste of time that is.
Hashtags also help speed up the virtual equivalent of passing notes around during a conference. It seems a bit subversive, somehow. I can't wait to try this one out.
Twitter disturbs me less than Facebook. It seems that you can put your tweets out there, anonymously and without all that 'friends' or 'friends of friends' or 'friends of friends of friends' palava. It's possible to 'follow' and 'unfollow' others on a whim. I like that, and can see how it can be used as a tool to promote products (several publishers) and publicise services (OU_library). Stay focussed though, or I'll unfollow you.