I had my first official tickling session a while ago with Ice Princess, and I was surprised to find out that my feet are barely ticklish at all. When she tickled them, it gave me a tingly feeling, but it didn't make me want to laugh. It made me want to grit my teeth. She got good reactions from my upper body, though.
And honestly, if what I see in tickling videos is any indication, the feet seem to often be the less ticklish part of most people's bodies. Most 'lees in videos seem to have stronger reactions when tickled in various parts of their upper bodies as opposed to their feet. Maybe that's just want I tend to notice, though.