You have to hand it to Dopplr, they have some pretty sweet features included in their service like Carbon Footprint calculations, travel tips provided by third parties like Mr & Mrs Smith Hotel Collection and telling me when my friends are going to be nearby. The other day they sent me my 6 month travel report too which provides a really nice graphical representation of my travel timeline – check it out here: http://reports.dopplr.com/2009/c65e791a5db1713a.pdf
My other favorite travel service is Tripit which has probably the best feature of both service – the ability to email them direct with my travel receipts from American Express and have them create a detailed travel itinerary, automatically – neat.
Feel free to add me on Dopplr or Tripit!