Here's an example of a fat tweet so you can see what it looks like.
And here's a screen shot in case at some point in the future that gets truncated (as it seems likely it will).
2. When it displays a tweet with a url that was shortened by t.co, it expands the url, so you get to see the url it is pointing to. That way you know in advance where you're going. This is a good thing, it's one of the nice things about the web that url-shortening screws with.
Update: I whipped up a little web app to show how it works.