Update, as promised...
Objective
Documents and paperwork requirements remain as before - no change. All visitors to the USA, entering by air without a US visa in their passport should complete an ESTA form online, and also the I-94W. Customs forms continue to be required (and will be so into the future) for each surname/family name travelling.
There is a grace period and amnesty for non-completion of ESTA in effect. The duration of this period has not been advised.
Subjective
US immigration and Customs officers and procedures continue to degrade international respect for the USA at a rate that is invisible only to US lawmakers: Only Iraq (and arguably Kyoto) have the capacity to madden non-US citizens more rapidly. I'm not exaggerating - I see the results by the thousand quite regularly, and often have to advise customers not to express their real opinions to officers on arrival . I love the USA with passion - always have: It saddens me to see the country I love diminish its' own reputation abroad quite so unnecessarily.
The ESTA implementation has been frankly chaotic - communication, IT and management of the project have all been sloppy, leaving a wake of confused and irritated airlines and passengers who are still waiting for clarification and deadlines. Depressing, and avoidable stuff...
EDIT
P.S. - Just for good measure, due to another error by US Immigration, there are currently two different printed versions of the I-94W in circulation - there are slightly different questions on each one. Immigration have given a dispensation to airlines to use the newer (incorrect) version that Immigration themselves distributed, in parallell for a period of time that has not been specified.