To this end, we moved our "Get AddThis" process up to the front page of the site, and made registration optional (see our home page above.) Also note that the decision to "Register" was positioned as a value proposition: Do you want analytics? Create an account, it's easy. Just want to share? No problem, enjoy!
[Ed: Yep, that's our Halloween logo- check out how our very gifted lead designer Jeff Wong ran a little impromtu contest to decide what image to use.]
We tested this approach to a limited set of users, and saw a dramatic increase in usage and some very positive feedback. Not long after that, we rolled out the change to everyone. The end result was an enormous increase in usage of AddThis, and a higher registration-complete rate, because the users that started the registration process had a reason to complete it beyond getting over a barrier to entry.
For more examples, check out Sasha's excellent Posterous article below:
Designing for social traction: Turn a user into a passionate customer *before* making them sign up for your service - Sachin's Posterous
And Happy Halloween!