This seems weird.

Why would I login and tie this to my Facebook account? Why not an e-mail since I'm making purchases through that?

If anything, I'd rather install something in my Gmail/Yahoo account that basically had a one button click mechanism that shows up when the app reads that the e-mail address/subject is a receipt (especially with common online companies like Ticketmaster, Amazon, FreshDirect, airlines...) I don't want to have to remember to forward it to a certain e-mail address. I'd rather the app say, "hey, this looks like a receipt, would you like to archive it?"