While I agree with Arne, and put the string in the first joint of my fingers myself, other people have successfully used different locations.
For example, Rick Welch puts the string on his fingertips, as your friend suggests, and has been very successful in winning tournaments and taking game with this method.
Historically, I believe the string on the fingertips has been more common than it is today. For example, in Horace Ford's book, he recommends putting the string on the fingertips.
Other people hold the string so that it rests between the first two joints. How they manage to shoot that way, I don't know, but I know people who swear by and shoot very well using that placement.
As with many things in archery, one size does not necessarily fit all, which is one of the things that makes it interesting.