The problem with many of the "press release" websites is that what they expect are corporate announcements, not news releases. I even had a news release refused at one of the big sites not long ago because it contained news (a few topline facts from a survey, with information on how to get the whole report) rather than a corporate announcement.
OK, I'm through venting.
As far as articles are concerned, the worse thing that can happen is that the duplicate content filter will smoke some of them from the SERPs, but that's only if you automate the submissions. Automation leads to:
- identical headings
identical title tags
identical file names
If you hand submit, the articles won't be the same on every site, will they? Unless of course you manually replicate automation.