Georgia. If you're on Windows or Mac, you should have this pre-installed.
There's an expanded version called Georgia Pro; however, it'll set you back a bit of money if you want the light version. The version of Georgia that comes with OS X and Windows just has Regular, Bold, Italic, and Bold Italic.
Isn't that just a regular tweet ?
Don't know, mate, I don't use Tweeter
All times are CET. The time is now 20:43