Ask HN: When do you say "enough is enough" and just ship it?

I've been developing my first web startup (foldr.co) since winning a startup competition in late February, and while I've made a huge amount of progress, I have an ever-growing list of "must-have" features and design changes that come from interviews with alpha testers and potential users.

I know I should launch as soon as possible, but I'm also keenly aware that any drastic changes to design or functionality might upset users. I'm experiencing an incredible amount of anxiety on this front...so much so that I opened registration to make myself feel like I had "half-launched". How those of you with experience launching startups convince yourselves it's time to temporarily stop development and ship?