[goldfish]

You can enter multiple airports (as long as they're in the same time zone). Just separate them with commas.

[raldi]

Have you considered watching to see if a user searches for, e.g., flights out of JFK immediately after an identical search for flights out of LGA, and then gently highlighting the feature?

[PompomCris]

There're a slew of new flight booking startups like http://wuhutravel.com and http://sillk.co that I believe are trying to entice younger travellers by apparently launching features like you just mentioned raldi (based on screenshots I've seen on dribbble from their designers)...

[bgruber]

i'd like to reiterate that hipmunk should make it clearer that multiple airports is supported now. It used to not work, and therefore I used Kayak.