Do co-founders usually live nearby each other or is it okay the be far away partners?
My experience has always shown that working together with a co-founder remotely is extremely difficult. It's analagous to trying to make any sort of long-distance relationship work. As we all know, these kinds of relationships fail more often than not.
If you are organized, diligent, and can communicate well, you will have any problems working remotely. Time zones can sometime be an issue, and not locking down the requirements can also be an issue. But as a software developer, I have been successfully at working remotely since 2003.
This is a conundrum. The value of being in the office together is huge. Sometimes it cannot happen (I currently commute ever week from Seattle to LA). If you do not all live in the same area then you must get together often. If this is not physically then even more often. That said, I have seen teams that work so badly together, being in the office made it worse.
Buffr do quite well remotely. You need the right people for remote to work though.