I am drawing up my second press release, the first one last december, 2007 so I am not doing very many, to say the least. I am finding in my niche that competitors are often using PRWeb for their once or twice a year press release with all the bells and whistles, photos, logos and more of the "I have something important to say" content. Additionally they are using the "lesser" press releases such as prnews now and prleap. No disrespect to them as they may be as "good" as PRWeb as far as I know. They are using these other pr sites for shorter, less news worthy releases resulting in 4-6 releases and more in a year. I have a lot of "news" to release so do you see a problem in this approach or is it spam, nearly spam or just not good practice?
Submitting press releases is a great marketing strategy. You should follow the strategy used by your competitors. Bigger websites like prweb typically only accept high quality press releases that are actually news. I had a press release declined on there because they couldn't verify the information, even though it was completely true. The more press releases you get out there, the more links you get and the better chance you have at getting written about by some type of news company. Of course, avoid submitting a press release if the 'news' item would not be of interest to anyone at all. With that type of press release, even if it gets you links it could also harm your site/company reputation.
If I had the budget, I think I would do 2 per month in my niche and target different keywords, and use a prweb paid option (like $100-$250). I'm not sure how big a difference some of the pay levels make...wish I knew...I will probably just use $80 option as their bells and whistles ones aren't cheap