Gamification is about changing behaviors by allowing people to do that in a gameful way. LinkedIn uses a progressbar to nudge people into sharing more information. Some people get really into it to get the progressbar up to 100% and feel competitive.
A progressbar caters towards the fun motivator "Achieving a sense of completion." So this examples points in a right direction, though you could make it a nudge more gameful, e.g. by using whimsical percentage titles (80% = Writing Hero) etc.
My landmark book on gamification in the enterprise was just published and I am talking extensively about intrinsic/extrinsic motivations, the problem with rewards and competition, and how to tackle blue collar workers. Exactly all those questions that you raise. And with tons of examples.
BTW: if you want to learn more about progress bars as used in gamification, check out our Enterprise Gamification Wiki: http://www.enterprise-gamification.com/mediawiki/index.php?t...