This study ($30 for full text) looks into the factors impacting PDA adoption in health care.

Major barriers to adoption were identified as usability, security concerns, and lack of technical and organizational support. PDAs offer health care practitioners advantages to enhance their clinical practice. However, better designed PDA hardware and software applications, more institutional support, seamless integration of PDA technology with hospital information systems, and satisfactory security measures are necessary to increase acceptance and wide use of PDAs in healthcare.

The best study I've seen on this is Mobile Computing in Nursing, by Spyglass Consulting. At $1,495 its a bit pricier than the study above, but if you're a vendor looking to develop a product, its a steal.