I always was a fan of Dopplr to the point where I've put all my trip since birth more or less into the service. I was mainly using it for insight and statistic about my past and upcoming travel. Like knowing the last time I've been to Paris or Brussels. Although, they were bought by Nokia and dead since then, the service was still working till this summer. But then something broke in their system and you couldn't add new trip. Thus I was challenged to find a solution and I did build a rails app prototype and an iphone app as well. The iphone app can import dopplr trips and is totally autonomous. It is very basic right now but I plan to improve it if I've got enough time. One of the key feature I use, is that it export my trips to my calendar, thus I don't need to enter them again. Here is the current design:
I'm not sure there is a market for dopplr nostalgic and probably most of their users migrated to other services. But if you're interested or have a better solution, get in touch
While writing this, I've checked the dopplr site. They are killing it the 1st november. I guess it is the end.