[icarus]

I went to Letterman. I filled out the form on the website and they eventually called me to tell me I got two tickets. The day of the show I went to the box office with a group of friends and they all ended up getting tickets as well without having to do anything in advance. There was a group of about six of us who went.

So if you don't have tickets before you go, you still might be able to secure some on the day by just walking up.