I'm not a Costco member, but I've been thinking that membership may be worthwhile just to get the benefits offered by their American Express (aka TrueEarnings) card; the Capital One interest bonus may be an additional incentive provided that a) its rates stay competitive, and b) you're not a rate-chaser.

Here's my thinking on the card...as I understand it, the TrueEarnings card serves as both your Costco membership card and a regular Amex credit card that's usable anywhere, so that you get two uses out of a single $50 annual fee. Then, the Amex card offers 3% cash back on gasoline and restaurants, and 1% on everything else. In my case, this means that since I already spend more than $1,667 annually for gas ($32/week) commuting to/from work, I get my membership fee back by doing nothing more than what I'm already doing anyhow. Is this sound reasoning? Are there any gotchas I didn't think of?

Anyway, here's a link to the Costco Amex page: http://www.costco.com/Service/FeaturePage.aspx?...