Wonderful UX with this, very simple and efficient, took less than a minute for me. The only thing that could make more sense is to upload the photos oldest first.
We're currently experiencing an uptick in users right now, so it's not uncommon for some users with 2,000+ photos to take about 15 minutes or so to sync.
Edited: Yeah, we're uploading the newest ones first. We may look into changing that tonight sometime when we get a chance. Sorry for not clarifying that anywhere.