Relying on the the platform to handle the user authentication and document storage is something I wouldn't be comfortable with, though I'd use it as an option (as facebook connect, google or any other authentication service out there).
In general, I think this would have been a hit 5 years ago. Now, with services like heroku, phpfog, app engine, even github having free plans, the "hosting" part seems to be solved, and something pretty similar can be done these days with some sparkle from FB Connect and a bit of rails/php for the client side storage.
Don't get me wrong, I like this kind of services because [I think] they push innovation in different directions. It's just that I think there are a few pretty well stablished and provide similar (or equivalent) functionality and I just don't see any obvious advantage between this service and the others, though I see a few drawbacks.
What should I review? There's nothing on it.
There's no About section
No Register link (though http://www.sephid.com/sp/register/ works)
The register didn't worked (error 500)
There's no visible functionality other than a search of 2 sample data items
Once you login (the register DID worked, even returning a 500 error) there's nothing you can do other than search those 2 sample data items.
The search functionality has a green-ish box (while it's retrieving the search results) that flashes for less than a second, making (if possible) the dead simple and only functionality of the site (search 2 sample data items) something somehow confussing (what it was saying? something relevant? why some elements danced in the page while the search was performed?)
My review? That I spent more time reviewing the site than the time it took to build it.
My advice? Put your shit together, plan more, add some useful functionality, test it and come back again.