Nomadico is a new weekly newsletter with tips for working travelers. (It's published by Cool Tools Lab, which I run with Kevin Kelly). In the latest issue, editor Tim Leffler recommends a Twitter account called Secret Flying:
For "mistake fares" and airfare clearance sales, follow @secretflying on Twitter. Recent round-trip deals — which you have to act on quickly — were Orlando to Lima for $261 round-trip on Copa and London to the Netherlands for only £8 roundtrip. There's a U.S. and European version.
