Info on this service from Turkish Air's U.S. website includes this note for U.S. citizens:
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Please note: A Turkish Visa ($100) is required for U. S. Citizens that wish to use this service as they are leaving the transit area of the airport facility. Visa requirements vary for citizens of other countries.</font>
Link (Scroll to bottom)
It's probably worth the $100: Atatürk is nice, but not 10-hours nice after a 9-hour flight (or more if you're departing ORD).
[This message has been edited by Y_me? (edited 10-15-2003).]