Did you try not requiring sign ups to respond? Invitees should be able to click yes or no and automatically create an account for them.
In the event invite email you could have a short message that tells the person can just reply to the email with a 'Yes/No/Maybe' in the subject and any thoughts or questions in the body. The service would then show the appropriate response on Julie's event. 'Maybe' responses would be marked somehow to show they need manual review and Julie would be able to see the the response text from the email and easily set the status for that person.
To help make it simpler, for people that don't change the subject you could default to a 'maybe/review' response or try language processing on the response text.
Combine this with your idea of including links in the email for a quick response and I think it could work.
We chose to get it out the door first so we have a larger user base to learn from, but hopefully we'll get to it soon.
Great suggestion!
Why would a person go to the trouble of filling out everything on WhereBerry, connect their Gmail, connect their Facebook, go through both lists, etc.? The only thing WhereBerry has done is introduce an extra step without adding any incentive to do so. The event host is still getting the same information that they would if they posted on their FB wall, or shot an email out.
I hate beating up on WhereBerry, but this is just the tip of the iceberg when it comes to figuring out this problem. We went well beyond these first steps and still didn't figure it out.