As per my knowledge if you do paid PR then it will be covered in other PR sites but for free PR i cant say yes.. But for some good sites like PR log etc the free one is also covered by other sites.
Press releases are still effective, but you have to be careful and consider Google's link schemes update. If you choose to submit your PRs using free services, make sure they use rel="no follow" tag for the links and avoid over optimized anchor texts. Here is an interview about online press releases best practices - http://www.advancedwebranking.com/blog/how-to-use-online-press-releases-and-be-google-proof-interview-with-joe-laratro/