Back in May, my friend Stowe Boyd told me about an intriguing new Web service called Dopplr; since it was (and still is) operating as a “private beta” service, I relied on him to send me an invitation to join. And for the next several months, Stowe was the only other person on my Dopplr network, and I basically ignored it. But now I’ve got a dozen people (known as “fellow travelers,” presumably as a tongue-in-cheek reference to covert members of the Communist party in Joseph McCarthy’s day) in my network, and I’ve sent invitations to another 20 people. And while it’s not going to cure cancer or bring about world peace, I think it’s sufficiently noteworthy to … well, to write some notes about it. So here goes …

Fundamentally, Dopplr encourages you to create some basic information about a trip that you intend to take, at some point in the future: where are you going, when will you leave, and when will you return? You can also write a note with as much, or as little, additional information as you want. All of the other Dopplr users do the same thing; and, as you might imagine, Dopplr provides you with the ability to look at your network — i.e., the people you’ve identified as fellow travelers, and who have identified you in the same fashion — to see where they’re going. If a fellow traveler indicates that he’s going to be visiting Olympia, Washington (as I will be next year), and you have no idea where that might be, you’ll see a helpful hyperlink that will show you the location on a map.

Why would you bother with any of this? Well, Dopplr turns out to be a great way of dealing with the “ships passing in the night” phenomenon: all too often, we compare notes with friends or business colleagues (who might live in the same town that we do, or might live on opposite sides of the country or the world) and discover that last week, we were both in the same city at the same time — probably for entirely different reasons, but with some free time in the evening (or perhaps only for an hour or two in the morning), when we could have gotten together for dinner, or a drink, or perhaps just a quick breakfast … if only we had known, in advance, that we were both going to be there. But by the time we find out, it’s too late. And so we say to each other, “Next time you’re going to be in X-town, let me know, and we must get together.” But we never do …

As such, Dopplr is a “micro-blog.” Sure, you can enter nauseatingly detailed notes about why you’re planning to visit X-town, what you plan to do once you get there, and all of the things you’re going (and places you’re seeing) while you’re there. There’s a Flickr connection so that you can see random pictures from X-town, and probably even post your own pictures, so that anyone else who shares a passion for X-town can see them too. You can display a map of all your upcoming trips, if you think other travelers will be impressed by the variety of push-pins on the global map (for example, here’s a map of my upcoming trips, between now and June of 2008):

There may well be a dozen other things you can do, as well, but most of them are irrelevant — and, I suspect, rarely used. The point is that it’s a blog with a single major objective: to share information with trusted friends and colleagues about the dates and locations of upcoming trips. Period. Hence the appropriate characterization that Dopplr is a micro-blogging service.Given the enormous fuss about “social networks” in recent weeks and months, it’s also worth noting that Dopplr is a social network, too. Obviously, it’s not the primary place where you would expect your friends to find the details about your current mood, your likes and dislikes, your favorite music, and your opinion of Paris Hilton. But informing friends and colleagues about the dates and locations of upcoming trips is, fundamentally, a social function; the only reason to bother with the exercise is that you think there might be an opportunity for a social encounter.

But this raises an interesting point: do you really want to spend a long, boring evening with a business colleague just because the two of you happen to be in Buffalo on the same Tuesday night in November? I didn’t even think about this until I happened to look at the Dopplr home page for one of the fellow travelers in my network, and was astounded to see that she had identified 310 fellow travelers of her own. “Egad!” was my first reaction. “I don’t even know 310 people!” But then I remembered that I have 9,000+ names of personal and business colleagues in my address book — so I’m not really that much of a hermit.

But my next thought was, “Egad! I certainly don’t have 310 friends …” Well, actually, that’s not true, either: there are hundreds of people I enjoy talking to on the phone, or communicating with via email, or chatting with briefly about some topic of common interest at a computer conference. But do I really want to spend an entire evening with them, over dinner at a mediocre restaurant in Buffalo, just because we both happen to be there are the same time? Maybe other people are more sociable than me; in my case, I’d rather have dinner alone, courtesy of room-service from the hotel kitchen.

When I thought about it from that perspective, the number of potential travelers shrank considerably — and thus far, I’ve only sent out invitations to about 30 people, each of whom I really would enjoy seeing for dinner, or lunch, or breakfast (as long as it wasn’t too early), or even a beer at the airport frequent-flyer lounge. And I guess that other people must feel the same way about me, because thus far, only 10 people have accepted my invitation … and nobody else in the Dopplr environment has asked me to become one of their fellow-travelers. Well, that’s okay; if Dopplr facilitates two or three pleasant encounters with friends and colleagues during the course of the year — encounters that would otherwise not have occurred because neither of us would have been aware we were in the same city at the same time — then it will have been well worth the cost …

Ummm … actually, the cost is zero; like so many Web 2.0 services these days, it’s free. While it’s in the beta stage, there are no subscription fees, and also none of the banner ads and Google Adsense intrusions that usually provide the business model for such services. I have no idea what Dopplr’s founders (who, according to the “about” page on their site, are from Helsinki, Finland) plan to do when they launch the “real” service, but that’s not my problem; I assume they’ve figured it out.So, how do you sign up for Dopplr? Well, if you work for one of the Dopplr 100 companies which includes companies like Google, Unicef, IBM, Wieden + Kennedy, Virgin, Louis Vuitton, The Economist, Apple, McKinsey & Company, and Nokia — you can sign up by visiting the Dopplr 100 page. Otherwise, you’ll need to find someone who already has a Dopplr user-id, and ask him/her to send you an invitation.