AA.com v FareChase (Score 2, Informative)

Since you mention that you may be building a screen scraper that gathers airline fares, you may be interested to know that American Airlines has already sued (and won a preliminary injunction against) a software company that built a tool that does much the same thing. The case is American Airlines v. FareChase, and was discussed on LawMeme:

American ... sued FareChase in a Texas court (American is based in Dallas, so that's its home turf) and got a preliminary injunction against FareChase's screen-scraping practices. The court decided that the screen-scraping constituted an "interfer[ence] with American's personal property," also known these days as a trespass to chattels. The court also noted that FareChase's actions might be a criminal violation of Texas Law, which states, "A person commits an offense if the person knowingly accesses a computer, computer network, or computer system without the effective consent of the owner." Tex. Penal Code 33.02(a).

The injunction order is posted on EFF's site, and the briefs are posted on Bag & Baggage.