I love human touch, and crave it. Tickling fulfills that in a big way. It is intimate, but as others have said so well, it may or may not be sexually intimate. Generally it has a friendly intimacy with friends, and the other kind with my boyfriend.
I have to agree wholeheartedly with the people who have been saying that with friends, it's fun..but with someone whom you share a romantic interest in (like say with me and my wife), it is very intimate and can go on to being sexual.