There is a nominal value in submitting your press release to places like prweb.com. I've successfully used their site to get a few backlinks that helped out, albeit only a small amount.
Another tactic is to use HARO to get your organizations message published.
The true value of a press release is in its news-worthiness. If your PR is just thinly veiled advertising, its not going to be worth much. If your PR is exciting and new, it can go viral and a press release service can help with the first steps to getting it there.