PREVIOUS ADVICE 
There's no question: the Internet has profoundly changed the way science is done. With instant messaging, email, and other newfangled communications tools, scientists in different parts of the world can carry on spontaneous conversations with each other almost as if they were in the same room, the only cost being the cost, if there is one, of an Internet connection.
For the first time ever a scientist can take advantage of a piece of scientific equipment that's on another continent, in some cases even controlling the instrument remotely. And while you're chatting with your international collaborators or running an experiment on a neighboring continent, you can also be making lunch plans, answering student questions, and coordinating with your spouse or significant other about who will pick up the kids from the after-school program. It is an excellent tool for collaboration, and, though its charms can sometimes distract less motivated students, the Internet has become indispensable in the modern laboratory.
An article  late last year in the Chronicle of Higher Education (subscription required) alerted me to a study carried out by Jonathon Cummings, an assistant professor at the Massachusetts Institute of Technology's Sloan School of Management, and Sara Kiesler, a professor at Carnegie Mellon University. This NSF-supported study showed that the kind of collaborations facilitated by the Internet?multiple-institution collaborations?produce fewer results than intra-institutional collaborations. The results are scheduled to be published this year in the journal Social Studies of Science.
This result is hardly surprising. Anyone who has ever been engaged in any sort of remote collaboration knows that there are obstacles. Working in different time zones has disadvantages. So does working at institutions with different policies. Sharing resources among institutions requires extra administrative effort, and thus consumes an extra chunk of the resources being shared. Internet-based white boards do exist, but few people use them. And they are hardly as effortless or immediate as an intense blackboard session with whatever fragments of dusty chalk just happen to be lying around. Most important of all, perhaps, is the loss of the more visceral aspects of human communication. E-mail is a poor substitute for a face-to-face chat.
Part of my job in writing this column is to point out things that are obvious once you think about them, but that, because you're busy doing science, you probably don't have time to notice or think of on your own. This is an example.
The fact that the average remote collaboration is less productive than the average local collaboration is not surprising, but it is worth noting and thinking about. Everything you do in your young career, every decision you make, ought to be based on a careful weighing of the potential costs and benefits. That doesn't mean you always want to play it safe; it means that you ought not to take gratuitous risks. If the choice is between a promising remote collaboration and no collaboration at all, join the remote collaboration and don't look back. If, on the other hand, you fully intend to be involved in some kind of collaboration anyway, but time, space, and funding limitations mean that you have to make a choice between long-distance and local, then give the matter some serious thought.
Long-distance collaborations can be a bit like long-distance love affairs: they can be good in some respects, and almost certainly better than nothing, but they can be painful and unsatisfying. There's something missing, if you know what I mean. My advice: If you can't be with the one you collaborate with, collaborate with the one you're with. Or something like that.
I read almost all of your responses and writings and think they are very helpful and inspiring in many cases.
I am a Ph.D. student at Tulane University in New Orleans, finishing up. I am thinking about continuing as a postdoc in the U.S. It is clear to me that the postdoctoral grants available to foreign nationals are very few and specialized, which puts me at a disadvantage.
My question is: If a PI has an NIH or NSF grant, is any of that money available as a salary for the foreign postdoc? If not, what do PIs normally do to fund their foreign postdocs, and is it a tedious procedure?
Thank you in advance.
All U.S. federal sources for the support of science and scientific training, including the National Institutes of Health (NIH) and the National Science Foundation (NSF), make a clear distinction between money set aside for training and money for research. Money for training?in the form of fellowships and training grants?is reserved for U.S. citizens, permanent residents, and a small group known as "non-citizen nationals," which I think means people from Guam and Puerto Rico. Money for scientific research, however?R01s and other NIH research grants and research grants from NSF?come with no such restrictions. As long as your visa status allows you to work as a scientist, and you meet all the technical requirements, U.S. academic institutions are free to pay your salary from research-grant funds.
Glad to be of use?