Turns out that TripIt is pretty good at parsing emails -- such that it's better to just automatically forward airline confirmations to them (plans at tripit.com) and have them make sense of them.

Here are the rules I've setup in Gmail to do my dirty work:

TripIt

Matches: from:(support@tripit.com)
Do this: Apply label "Travel"

Alaska Airlines

Matches: from:(Alaska.IT@alaskaair.com) subject:(Alaska Airlines/Horizon Air Confirmation Letter)
Do this: Forward to plans@tripit.com, Apply label "Travel"

Expedia

Matches: from:(travel@expedia.com) subject:(Expedia travel confirmation)
Do this: Forward to plans@tripit.com, Apply label "Travel"

Orbitz

Matches: from:(travelercare@orbitz.com) subject:(Your Itinerary)
Do this: Forward to plans@tripit.com, Apply label "Travel"

Matches: from:(travelercare@orbitz.com) subject:(Confirmation)
Do this: Forward to plans@tripit.com, Apply label "Travel"

Southwest Airlines

Matches: from:(SouthwestAirlines@mail.southwest.com) subject:(Ticketless Confirmation)
Do this: Forward to plans@tripit.com, Apply label "Travel"

United

Matches: from:(UNITED-CONFIRMATION@united.com)
Do this: Forward to plans@tripit.com, Apply label "Travel"

Virgin America

Matches: from:(no-reply@virginamerica.com) subject:(Virgin America Reservation)
Do this: Forward to plans@tripit.com, Apply label "Travel"