Cameron,
A main objection often heard about this is the additional burden on the researchers to deposit raw data. I have to admit that I would not be enthusiastic to reformat all of our raw data in a form that complies with a journal's requirements for supplementary information. However it costs me nothing to provide links to our live lab notebook pages (which will be edited as new information comes to bear. Of course wiki page versions keep track of when this new information gets added.)

This is really a key selling point of Open Notebook Science: researchers already have to keep a lab notebook so there is really no fundamentally new burden involved. In reading the difficulties reported by some people concerning the time burden of ONS, it is generally not about the core ONS concept but about related activities, like re-writing and re-formatting lab data for consumption by larger audiences. Yes, I do write summaries of our projects periodically on the UsefulChem blog but that is not an essential component of ONS - the lab notebook pages on the wiki are sufficient.

As we move towards more automation it will become increasingly difficult to have people write detailed summaries of what is going on as it happens.