I travel a lot for work and fun. I tend to book trips on the individual airline's websites (after I use Farecast and SideStep to find the best deals), so I get the mileage bonuses. The pain of that is that you get all of these different confirmations, emails, and tracking numbers, so it's not easy to consolidate them down to my schedule. I use TravelTracker for the Treo to type it all in, but it's time consuming, and annoying.
Enter TripIt. That email confirmation you got? Forward it to firstname.lastname@example.org. In under a minute, you head over to TripIt, and you get this:
Want to add more to the trip, like a car rental? Just forward it on, and TripIt adds it to it. Want to track some activities you want to do while on the trip? Use the TripClipper to bookmark it to your trip.
I like the service a lot: they focus on ease of use and solving a problem. There is definitely room to improve here, though: syncing with Outlook or Google Calendar, for instance. Consolidating Frequent Flyer accounts is another area they can help with. But for sheer, purpose-driven Web 2.0 approaching a difficult problem with a cool effortless solution. it works.
I have 5 invites I can give out if you're interested in trying it; let me know.