And you have to account for indexes, temporary tables used for data analysis, etc. And most of it is probably not compressed. So with that perspective it isn't that much data at all.
That's an incredibly large amount per user? I have worked on a couple online dating sites, including one that was fairly popular (Let's Date - which stiffed me for my last invoice before they went belly up grrr). Unless you're storing images in the database, it's really hard to generate 600k for a dating workload - even with indexes.
The only thing I can imagine generating 600k per user is putting something like "hit tracking" in the database. Which I've done - yes it adds up - but it's also relatively easy to move to some other kind of store.
That's really a good way of looking at it. I though it sounded like a lot of data, well, 600kb is a lot of textual data, but who knows what they have stuffed into the database.
I worked for an e-commerce site, with a few million customers, even more orders, data-duplication all over the place, and still we where using a perhaps a 200GB of database storage.