The OA movement has three important "side effects":
1. Pioneered by PLoS ONE, many OA journals have removed perceived "impact" as a review criterion
2. Pioneered by PLoS ONE, many OA journals are mega-journals where the appropriateness of the topic of the manuscript to the journal is not an acceptance criterion.
3. Most OA journals allow you to make your manuscript public prior to submission
I have found that points 1-2 has made my research much less risk-averse. I can focus on truly challenging and long-term research questions without worrying whether or where I will be able to publish. Before it was: "In order to do X I have to do Y and Z first, but where will I publish Y and Z?" or " If I manage to do X and Y this will sail in to Journal Z". Now it is "It's important to find out about X; let's try it and publish what we find".
I can share our work at any stage in any way I see fit. We put all our manuscripts, MS and PhD theses on preprint servers such as arXiv and we get a lot of great feedback long before the "official reviews" arrive.
It still puzzles me when I see tweets like "Manuscript submitted to X!" and "Paper finally accepted in Y!!!" without a link to a preprint. What's the information really communicated here? "Hope to score a publication point soon!"? and "Another line on my CV!!"?
Of course "The people who payed for this research should be able to read about the results" is still a major factor but it has become so much more.
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