A club membership shines during "service interruptions": cancelled flights, weather at the airport, etc. The club customer service line is rarely longer than the one outside of the club. Having a quiet place to work or read can also be worth its weight in gold.
As FTraveler said, if you fly with CO or NW, look into an Amex Platinum Card. The Platinum Card comes with same day NW/CO lounge access, and the $300 fee for the card ($225 if you have an Amex or Fidelity brokerage account) is usually less than buying a lounge membership.
[This message has been edited by skofarrell (edited 01-07-2002).]