We have recently updated the chart showing the growth and fate of OpenDOAR suggestions over time:
The overall annual number of suggestions has grown steadily, but the rejection rate has remained steady at about 22% of suggestions. There was a significant problem with spam during OpenDOAR’s first two years. We added spam blocking functions to the Suggestions form in 2007, which significantly reduced the amount of spam received, and which seems to be staying at a reassuringly low level.
See http://www.opendoar.org/suggestionschart.html for the chart full size and for further information on the various reasons for rejection.