I am positing here some of my opinions about Open Access journals.
One reason to publish in Open Access journals is that they generally allow one to publish complete scientific stories, rather than restricting the length of articles simply to make the publishers more money. For example, here are some comments I made in a online discussion about a lame article in the journal Nature that basically invented problems occurring with some Open Access journals:
As a follow up to Deltef's comments. PLoS journals and many other Open Access journals allow you to publish complete stories because most do not have arbitrary restrictions on the lengths of papers. I have been involved in dozens of publications associated with genome sequences, many in Nature and Science and now many in PLoS journals. For papers in Nature or Science we almost always had to make the stories incomplete because of page restrictions. For PLoS journals, we could tell the whole story. Note - PLoS does not encourage run on papers - they just allow one to include the material that is scientifically relevant.
Compare and contrast our genome papers in PLoS journals:
Life in hot carbon monoxide
With those published in Science or Nature (I only publish in Open Access journals if I have a choice but for these I was a middle middle author):
Based on this difference alone I prefer to publish in PLoS journals every time. Note that this may in fact make it more expensive for PLoS to publish those papers and thus I am more than willing to pay for that cost.