Last night we launched a brand new Twitter (which is now officially Twitter, not Twttr).Besides lengthening the name, we gave it a fresh new visual design, with the help of the highly talented FutureFarmers / Amy Franceschini and made a bunch of tweaks, so it's hopefully easier to understand and use.
Read more and give feedback at the Twitter Blog.
(Also, sign up and invite your friends—it's funner than you think. :)