You will be misunderstood
I typically write posts that are three to six paragraphs long. I try to be clear and direct. And yet, just about everything I write is misunderstood by someone. (Not the same someone, alas). They write to me and I try to explain.
It's hard to imagine how one could write something that 100% of the recipients will understood as written. If you overwrite to satisfy the last 1%, you're going to bore the rest to tears
All of which is a way of warning you about [a potential pitfall of] microblogging (Twitter, etc.). If you've got 140 characters to make your point, the odds are you are going to be misunderstood (a lot). There may be nothing wrong with that, but you should be prepared for it to happen. And most of the time, people won't take the time to ask. They'll just assume you're an ignorant jerk and move on. [Please understand (yes, I was misunderstood!) I'm not throwing the baby of microblogging out with the bathwater... I'm merely pointing out that the medium has to be appropriate for the message. Using microblogging (like Yammer) to share your quarterly review or to fire someone or to make an important, nuanced announcement is just sort of dumb. Using it for keeping in contact with an ever-widening circle of friends and colleagues is brilliant].
If it's important, or controversial, I don't think I'd obsess about making it short.