Achievement systems have 2 issues:
a. users attempt to fixate on achievements more than the software they're supposed to be using
b. users cannot achieve certain things, realize that its hopeless, and lose interest in the system all together and possibly the software
Yes, there are some interesting side-effects when you attempt to motivate people to do very specific things. But, I don't think people leave the site or software when certain badges are too hard.
I think http://www.StackOverflow.com is a good example of where badges only add to the experience and don't get in the way.
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Achievement systems have 2 issues: a. users attempt to fixate on achievements more than the software they're supposed to be using b. users cannot achieve certain things, realize that its hopeless, and lose interest in the system all together and possibly the software
Yes, there are some interesting side-effects when you attempt to motivate people to do very specific things. But, I don't think people leave the site or software when certain badges are too hard.
I think http://www.StackOverflow.com is a good example of where badges only add to the experience and don't get in the way.
The right set of achievements paced correctly can counter your second point. The first is quite valid, though.