[dstein]

I'd put Airbnb as a competitor to hostels, they're not really competing with Craigslist directly.

[nedwin]

It's easy to look at the problem with Craigslist and think that to challenge it you should build something which does everything that Craigslist does.

AirBNB is a competitor to Craigslist in that it is helping to take it apart piece by piece. Hopefully other YC companies will take on other categories / pieces

[qq66]

They're competing with a specific part of Craigslist, namely short-term accommodations.

Other companies are competing with other parts of Craigslist (e.g. StubHub)

[voidfiles]

Funny, because they seem to get quite a few referrals from craigslist.

[oscilloscope]

Wikipedia gets quite a few referrals from Google. Are they direct competitors?

[astrec]

That depends on your view of Knol.