With the Excel metaphor, I wonder if a better comparison might be craigslist. That's more of a utilitarian swiss army knife that's generally overlooked, but which a lot of social services are indirectly competing with.
Many a start-ups have come and gone trying to revolutionize house/apt hunting. If they try to incorporate craigslist, craigslist shuts 'em down; if they try to get organic listings, craigslist beats 'em.
Out of curiosity, why craiglist and not ebay? Is ebay "too big" (you're not advertising to people in your city, that you can meet and do the handover in person, but rather to the world -- and will likely have to deal with shipping)?