Always delete your cookies before checking prices on an airline website too. They do keep tabs on you.
Example: Buddy of mine working in Toronto, on Rte, Independent etc websites everyday, quoted over a grand return on all 4 airlines serving YYZ on dates he looked at (about a weeks notice). Deleted his cookies, quoted €510 by EI and ROU, slightly higher for the other 2 on the same dates. Dirty barstewards.