I realize that I can reprint a press release on my site as long as I copy it completely, but am I allowed to read a press release and then comment on it on my site, with the release as my only source. For instance, let's say that Microsoft puts out a press release saying that they just bought Google, can I write an article on my site that states my opinion on the purchase?
Yes, you can comment on them. You should link to them if you do that though, so people know what you're commenting on. And you don't have to copy them completely. That's just the "lazy" route, and there's actually a lot of debate on the issue in the PR community about that. No one's really going to stop you as long as you're covering a story though, but they're actually intended to give you info to write your own story or post as opposed to using it as-is.
Press releases are made in order to get publicity from the internet world ,you can definitely copy the part of press release and merge with your own view and thats it .But don;t just copy the whole release .. What you can copy according to copyright rules: The facts and figures The quotes said by people
Actually, press releases are "made" to disseminate news to the media, and now a more directly targeted audience as well. Press releases in and of themselves have nothing to do with the Internet.... that's nothing more than a distribution channel. The copyright rules with press releases are what's pretty heavily debatable in the industry right now. It's generally accepted that if it's posted as a public release and not before an embargo date that you can publish it. If the company only publishes it to a mailing list or on their corporate site though, don't assume you're allowed to post it as is.... the terms would depend on the company. Sites like PRweb and such have their own terms though, and generally the person submitting a release will have to give the right for it to be republished.