I'd say anyone that is mediating the bridge between cryptocurrency and fiat is the person who is helping the most with mass adoption. Exchanges, crypto debit cards or anything like that. If it's easy to buy and use them it's easier for people to wrap their head around it. I'm assuming when bitcoins do become mainstream they'll be very very easy to use by then and will be a little more similar to our traditional fiat spending is. Debit cards, possibly credit cards and smart people can hold their own bitcoins but people who don't understand them will be able to store them somewhere and pay a fee to store them there or of course that institution could lend them out and we'll all get screwed over when that ponzi fails. History usually gets repeated. It's unfortunate but true.