The International Journal of Medical Informatics reports a seven year qualitative study (full text $30) of 4 successful CPOE implementations. This is was a local effort, lead by Joan Ash of OHSU's Department of Medical Informatics and Clinical Epidemiology.

A multidisciplinary team of researchers studied CPOE implementation in
four organizations using a multi-method approach to address the
question “what are the success factors for implementing CPOE?” Four
major themes emerged after studying three sites; ten themes resulted
from blending the first results with those from a fourth site; and
twelve principles were generated when results of a qualitative analysis
of consensus conference transcripts were combined with the field data.
The study has produced detailed descriptions of factors related to CPOE
success and insight into the implementation process.