Neat idea. I love that the repayments are going back in to funding Zidisha itself - a unique way to raise ~$100k! Congrats on the funding round Julia :)
The model has been around for a while - you should give it a go! Your execution will be different and could be more successful. You'll learn a ton in the process too.
I remember an email version of this app about 10 years ago - I loved it for a bit surreptitious flirting at school!
The app looks really great and the signup process is straightforward with clear CTAs. Alas the FB integration makes it rather slow (maybe I have too many friends? ;). It seems to loads friends each time I open the page - could this not be cached? It took me a moment to realise the grey box was a friend selector; it might help to make it white and give it focus on page load. It couldn't seem to grab my girlfriend's email address and asked me to type it in (making me wonder why integrate with FB at all).
There's no way for me to share content on either FB or Twitter. I'd be happy to post to my wall (and tweet) that "I just adored someone with adore.ly".
If you're trying to build up UGC then I'd happily rate a few anonymous adores and I'd be interested to see the wittiest/cutest ones.
For user retention, consider email updates: 1. thank you for signing up, 2. thank you for sending your first adore, 3. it's been a few days, time to send another adore? And for the receiver: sending a second (and third) email a week or two later if they haven't clicked through to the site. The option to opt-out of emails is important but the granularity of notifications settings looks good. I also hope you have a Valentine's day promotion lined up!
I'd forget about making money until you have say ten thousand users and I'd remove the limit of three adores until then too. Then I'd limit adores (to 5) and users could unlock more adores using a platform like SuperRewards or FB credits.
If my girlfriend 'adores' me back then I'll get back with what happens...