I occasionally buy tickets for other people (often their only flight for a year or so). The Travel Bank program gives me a $5 per passenger kickback. This can make CO the best option, even when buying for non-status infrequent flyers.

Families of 5+ would also break even on a single round-trip flight per year. So if you take your wife and 3 kids to Disneyland, you have a reason to choose CO again even if it doesn't bring you anywhere near Silver.

The software can't be all that simple, since it breaks often. I've seen totally unrelated flights show up. One was a reused PNR (same as a flight I took about year earlier), another was a complete mystery: a flight between two small US cities I've never visited. I've also had flights fail to show up.

It's annoying that renewing early doesn't extend by a full year. (My Travel Bank was expiring in August 2009. I paid $25 in June 2009 and got renewed through until June 2010.)