Thank you to those who  responded to my inquiry regarding
ScienceXpress.  I was asked to summarize:

Libraries that have a subscription to ScienceXpress said it was mainly
because  users requested access.

The usage statistics provided by AAAS does not include "full text
viewed"  for ScienceXpress separately.  However,  responders with
ScienceXpress said their library’s usage of Science Online was high
enough to justify the extra cost.

Many commented that they disagreed with the subscription model for
ScienceXpress.  AAAS should include it as part of a Science Online
subscription instead of the library paying twice for the same content.
 A comment was made that there is only a handful of articles in
ScienceXpress, thus not justifying the annual cost.  It was easier for
the library to purchase the pre-pub article by credit card.  Another
said they were cancelling ScienceXpress due to budget cuts.

Thank you,
Liz Lorbeer
University of Alabama at Birmingham