As far as PLOS is concerned the editorial board seems pretty solid, at least I recognise several big names from my own field. In terms of money, there is still cash coming in from people wanting to publish in the journal, either individual payments to publish or large one off payments by institutions allowing all their staff to publish in the journals for a year (in the case of BMC.
PLOS also produces a print run of its issues which at the moment is pretty cheap compared to most journals, somewhere in the region of $160. One major advantage of the open access model is that you can simply download the PDF version of the article and keep it yourself and freely distribute it - legally, although I appreciate this won't help in finding old references several years hence.