There are also other things you could monetize that would make it easier for people to open their wallets.

Customization is probably a good thing, i.e. the subdomain and own-domain thing.

Physical stuff is always good, so I'd love to pay for an automatically created photobook/photobook-ready-PDF (I hate to do them in the crummy software supplied by the printer). Or, go one step further even and allow direct upload to Lulu. Basically a Make-your-own-coffee-table-book.

In any case, you might want to think about specifically targeting power users from the start, instead of going for the freemium market.