It's "funny" how often there are posts for "_____ is shutting down" for things that are completely new to me. I'll go to the page and (many times) think "I would have used it if I would have known about it!"
If you don't advertise well (and correctly!), you can't expect to survive, no matter how good your idea may be.
It was because they forgot to put an "e" between the "l" and the "r". For some strange reason, a lot of companies like spellr.com make that exact same mistake, and it always leads to failure.
If you still have data in Dopplr that you want out, now's a good time to migrate it to TripIt. Here's a simple script I wrote to do it. https://github.com/jlev/Dopplr2TripIt
as an extensive traveler, i experimented with in some years ago. it never really gave me what i wanted in terms of ease of use, nor did the community reach critical mass to yield good suggestions. gorgeous app, neat in concept, but it didn't really take off.
I think today foursquare does serve a lot of the dopplr niche. When i'm traveling and i check in to a new city, i find other folks who are in town. It's not so good for planning, but it works for discovering who's in town.
It would be interesting to graph SaaS products being purchased and then being closed down over time. It would be a good barometer of the skill levels of decision makers in acquiring businesses.
If you don't advertise well (and correctly!), you can't expect to survive, no matter how good your idea may be.