As of January 12, 2009 it will not be possible any longer to travel to the USA without an on line Travel Authorization:

1.WELCOME in many languages: https://esta.cbp.dhs.gov/esta/esta.html?_fl...BE-6E94DD3D6CD8

2. which countries participate ?

https://esta.cbp.dhs.gov/esta/WebHelp/ESTA_...aiver%20Program?

3. U.S. Customs and Border protection - Travel

http://cbp.gov/xp/cgov/travel/id_visa/esta/

LaoPo

It looks like to me it's just for people coming from visa waiver countries unless somehow I missed something

>>Welcome to the Electronic System for Travel Authorization Web Site. 

 

International travelers who are seeking to travel to the United States under the Visa Waiver Program are now subject to enhanced security requirements. All eligible travelers who wish to travel under the Visa Waiver Program must apply for authorization using the following process:

Select this option if:

You are a citizen or eligible national of a Visa Waiver Program country.

You are currently not in possession of a visitor's visa.

Your travel is for 90 days or less.

You plan to travel to the United States for business or pleasure.