You should really get this is you can. If you are United Global Services or American Express Platinum, they will even pay the $130 fee, but if you join GlobalEntry, then they will interview you and you can cross the canadian border quickly (Nexus) or use the fast line at the airport traveling internationally (GlobalEntry) and now with Delta, American and soon Alaska and United and USAirways, you will be able to use the short line. Here is how to do it:

  1. Apply to GlobalEntry
  2. You will get a magic number and card called the Known Traveler Number
  3. You then have to spelunk into your airline flight profiles and find this field (often next to the TSA Redress number)
  4. The airline then submits this to the TSA
  5. Find the magic entry (not easy!) at specific airports

For Delta, this in the About Me tab, go all the way down to the bottom to the Secure Flight Data area
For American, it is in and in the Customs and Border Protection field. At least right now, trying to enter something here fails.
For United, this is in the Profile tab of MyAccount, there is a small item called TSA-Prescreening Program and you enter the number under a plus sign (so not visible) and click saying you accept.
For Alaska, 

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