I have been playing around with services that help me keep track of where I am going and where I have been. So far, the standout application for me has been Tripit. You mainly use Tripit by forwarding the email confirmations that you get from various travel booking services that you use. Tripit parses through the confirmation email and identifies where you are going and when. It also is smart enough to put together several reservations as part of the same trip. For example, if I book a hotel for the January 10th and 11th and a train ticket that leaves on the 10th and returns on the 12th, Tripit knows that it is part of the same trip. I found the email parsing capabilities to be surprisingly accurate. I occasionally try to stump Tripit by forwarding emails from international travel or very small hotels. It almost always got it right. Recently, when using a client's corporate travel service, I noticed an option to add my itineraries directly to Tripit (see screenshot). I wouldn't be surprised if other travel services started to giving their customers this option.
Tripit provides a lot of upside for the minimal effort it takes to forward an email. For one, I get a nice little itinerary that I can print out. The itinerary has the address, confirmation codes, and telephone numbers of all the places that I need to be. It even has maps. I can also subscribe to an iCal calendar of my trips so everything is put right into my local calendar (I use iCal) along with my meetings. This helps prevent me from scheduling meetings when I am en route. My wife also subscribes to my calendar so she has all the details in her personal calendar as well.
The other service that I think I will start to use is brightkite. I will use this to post when I am at a particular place and I want to meet up with a friend. I like the features of brightkite. You can easily "check in" to a location either by address or by using a saved place (called a "marker"). Brightkite suppors a simple syntax that you can use over SMS. Plus you can Ping.fm to email in your location.
I have also tried Dopplr and Fire Eagle. Dopplr didn't do it for me at all. You have to manually enter your trips. I tried to have Dopplr listen to my Tripit calendar but it was horrendously inaccurate. Dopplr had me taking all these crazy trips to various parts of the world and treated lay-overs at different airports as discrete trips. It wouldn't be so bad if Dopplr was not counting my carbon emissions. I hated feeling defensive about all those trips I was not event taking. I closed my Dopplr account.
I am on the fence about Fire Eagle. I should feel very lucky that I have an account there. I hear that invites are very hard to get. But I don't feel like I get much value from the service. Fire Eagle can listen to other services to find out where I am. I have it listening to brightkite. There are a number of other applications which I don't use (like Dopplr, Plazes, and Navizon) that also talk to Fire Eagle. The only benefit that I see is that it gives Yahoo more information to serve me up better ads (which really isn't a benefit for me) and search results (but I use Google search).
So, for now, I am sticking with Tripit and brightkite.