I would vote it three and a half. The one and only reason I joined Twitter is to network for work purposes. Some people and companies just prefer Twitter. I've found that it's a way for me to get a hold of clients that are difficult to reach plus they can click on my LinkedIN profile for my stats.
I admit that I get extremely annoyed with having to abbreviate posts that are already pretty short. Probably more annoyed than I should but seriously, they need to increase the limit beyond one sentence. I do not like text abbreviations at all and having to spend extra time on making what I want to type fit without dumbing it down drives me nuts. (see, I could keep going. I'll stop, I've made my point- Twitter never would have allowed all of this)