We are human beings and it is only natural that we like to meet person to person, face to face. I can't argue with that as there is so much non-verbal communication that goes on that just can't be exchanged by other means.
Where is this going you may ask? I work for people all over the world, as is the nature of the internet. Most of these people I have never met in person. In fact in some cases I have been recommended by someone whom I have never met who also has never actually met the client in person.
So just how important is it to meet, properly? Not very evidence suggests. But, I still prefer, at least once, to meet those I'm going to work for in person. Firstly I believe I can make the positive impression that would be far harder to achieve by other means. The client, or potential client, gets to know what you're about and it definitely makes an enormous improvement as to how the future of any working relationship might go.
It does come down to that trendy term, non-verbal communication. It could of course work against you as it is much harder to make that initial first impression a really positive one. Personality starts to count, no hiding behind your website or twitter account. You will be taken at face value, can you handle that.
So when I hire someone it is nearly always someone I know in person, as a result I make a real effort to meet a new or potential client. Even if it's only managed the once, that 'once' is so important.