I just returned from ODTUG Kaliedoscope 2010, (awesome event, best one I have been to), and promised during my presentation that the Application Express 4.0 Web Services Evaluation Guide would be posted on the Application Express Web Services Integration page on OTN. Well it now is, so I kept my promise. ;)
If you missed me at ODTUG, you can see me give a very similar presentation this year at Oracle Open World. The session is at 12:30 on Thursday September 23rd, so don't get too crazy at the appreciation event the night before!
Update 7/28/2010: A patch set exception was created for the issue the Roel reported in the comments below. Log on to Metalink and search for 9848562.