I had this idea today - and should probably try to develop it myself but that won't really happen.  So - anyway I'm just going to leave this here and see if anyone will run with it.

You know those CoinStar machines in supermarkets etc?  (in USA afaik)  They convert small change into USD for a fee of about 9% - most of them now also have the option to buy various gift cards for the full value of your change (Amazon, ITunes, various restaurants etc...)

What if someone set up a venture to sell btc this way??  It's irreversible once the customer prints out the voucher - so no worries about chargebacks etc.  You could either print out both the public and private keys on the voucher or some redemption code valid on Coinbase or Circle or some other yet to exist site.  This would never be a way to buy large amounts of btc (or even other alt coins) but pretty much everyone has at least $50 in change laying around and a good way to get people 'on the fence' involved.

Anyway - it strikes me as a good idea.  Feel free to discuss and develop it.  I really hope one day soon it's an option to convert my spare change into btc!