Today RJ released a report on publishing in open access (OA) journals. It is interesting reading (for you who reads Swedish). RJ is a major research-funder in Sweden, and since 2010 they are rather persuasive to have researchers publish results from RJ-funded projects in OA journals. It appears as if 35% of the publications on research funded by RJ is published in OA journals, or journals with OA options. A descent number, but still far from 100%. The reason given by researchers on why OA is not used even more was a lack of suitable OA journals for the researched topics. The lack of high-impact OA journals and also the extra cost for publishing OA was also mentioned, but the latter two do not seem to be dominant factors.
I have two major issues with OA journals. The first one is the extra cost. The latest paper I was senior author on (and thus had to pay for) I published in a hybrid journal as an OA article. That costed me €4000 extra. €4000 is not toy-money, and provides a strong incitement for not publishing in OA journals. My other issue is the predatory journals. When publishing smaller studies in smaller journals, it is not always easy to single out descent OA journals from those that are only there to move money from libraries and universities to crooked editors. In the higher stratas that is not a problem; PLoS, Nature Communication, eLife, and many more are good journals (but expensive to publish in), but it is tougher to find the quality-journals in the medium and lower stratas (but there are several good there too, the BMC journals for example, are usually reliable).
I think 35% is good. It is likely lower for projects not funded by organisations that are strongly advocating OA publishing. But if a third of all RJ funded research is published using OA, it is likely that a descent amount of Swedish research in general is made public OA.