Most founders will tell you (and it's the stance that Y Combinator takes) that being in the same physical location as your co-founders is critical to success.
My co-founder and I seem to work very well at a distance. Frankly, I don't see the advantage to being in the same place.
Sure, very occasionally there are things that would go faster if I could draw them on an actual whiteboard instead of a virtual one. But these moments are rare.
Basically, I think virtual communication is something you learn how to do. Since we're not in the same location, we're very used to using tools and communication styles that provide the same advantage as being in a room together.
And there are many, many advantages for us to start an entirely virtual company. Primarily, when we do have to grow our company we're going to be able to hire the best people in the world (as long as they have a good Internet connection.) This seems like a huge advantage over Google, who can only hire the best people within an hour's drive of Mountain View. It opens up an entire new pool of talent for us.
Other advantages:
1. No rent for office space and no commute.
2. We can hone our communications techniques so that we're ready to scale when we inevitably need to have people in multiple cities working together.
3. People get to work in an environment where they're most productive.
4. We cover more of the world so one of us is usually close to an investor or customer that wants to have an in-person meeting with.
5. Since we cover more of the world the company as a whole has more perspective.
As to arguments on the other side, the only one I can think of is:
1. It's easier to communicate, and thus easier to get things done. (But with modern communications devices, e.g. a screen recorder to capture exactly what's going on my system so that the programmer can how I produce the bug, I remain unconvinced that in-person speed of communication is anything more than a slight advantage that is greatly outweighed by the disadvantages of not being an entirely virtual company.)
Are there other advantages to in-person interactions that I'm not thinking of?
David wrote the code for Basecamp in Copenhagen and I designed the interface in Chicago.
The distance was a big advantage to us. It helped us each focus on what we were good at without too much meddling. When you're close it's real easy to spend time worrying about stuff that doesn't matter. When you're further apart you tend to actually focus on the work since that's the only thing you can do.
Your mileage may vary, of course, but that was our experience.