(my friend, sadia asked me a question on twitter that I couldn't answer in 140 characters, so escalated it to email, and she said that I should post it to the blog, and who am I to refuse a request like that?)
I really like the open-source/federated microblogging site "identi.ca" which runs on the laconica platform. It's good stuff, but the user base isn't quite there (either on the site, or in the federated network.)
Basically the killer feature of microblogging, for me, is integration with a jabber/xmpp client, and pretty fine tuned control over who gets in your "stream/feed" Everything is nice, but fluffy (search, threaded comments, etc.) Jabber is great because it's so interoperable, and because jabber apps, like adium are killer robust and integrate well into the system, were as Adobe Air twitter apps (and even twitterific) don't so much. In some respects, it also boils down to the difference between pull (which is the typical solution, and not ideal) and push (which twitter can't cope with any more).
I have the attention/time to spare into this, if I can have a lot of control over what I see, and it's pushed to me live rather than via large regular pulls, it's easier to deal with. The end result is that while all the people I'm interested in reading/talking to are on the twitter, I have little tolerance for the site/service itself, particularly when I know that every other site does it a little better, and most can supply jabber feeds. This is a scaling problem, but Ev has cash, and the solution might be disruptive, but it's not conceptually difficult.
The thing is that, I think twitter is afraid that if they do anything drastic, and if there's any more downtime in a major way, that everyone will jump ship. And they're probably right. Which would be good for us, but not for them.
You also asked if microblogging was an addiction or curiosity, and I think I try all the new services out out of curiosity, but I don't think it's a particular addiction, aside from the general internet. It's sort of ironic, but I'd like to spend my internet time communicating people rather than reading the big portals. Hence the email lists, my "always on IM" M.O., ravelry, the fact that I don't really read the A-List blogs much, etc.
I was a big IRC user back in the day, and in a lot of ways I see twitter (et al) as an evolution of the IRC impulse, and while I don't think "going back" to IRC is the way to go (because frankly Jabber/xmpp is really a "better IRC" anyway,) so if it is an addiction, it's not a particularly new one.