The concept is simple. Copy Tripit on your confirmation emails and Tripit.com will read them and create an itinerary for you based on the emails it receives.
To get started just forward an itinerary to plans@tripit.com and it will do the rest. It supports a variety of itineraries already. To test it out, I forwarded a Southwest, Marriott, and Hertz confirmation emails and all 3 were successfully loaded into Tripit.
Check this list to see if your airline, hotel, and car rental companies are supported. They have all the major vendors so most frequent flyers will not have any problems.
Tripit.com also adds useful information to your itinerary such as weather and maps. Another useful function is the email interface which allows you to query and retrieve itineraries by sending an email with commands in the body. For example ‘get flight today’ will send you the itinerary for all your planned flights today. This should come in handy for Blackberry users.
Happy travels.