I have run across a problem with One Touch Dialing that seems to be a bug to me. I assigned Contact entries to One Touch numbers, however I got a message saying that they were invalid when I pressed the button. I had numbers set up as +1 (aaa) bbb-cccc. I read on the Nokia N8 blog that the phone cannot handle anything but numbers for a One Touch number. I could dial these numbers just fine from the Contact application but not as a One Touch number.
What I finally had to do is to reenter the numbers under a One Touch key without spaces or punctuation. One Touch dialing worked after that.