I don't get how really smart folks, folks trained to critically appraise actual journal articles, folks for who evidence is reported to be extremely important, regularly tweet out press releases without first having read the study.
Press releases are designed for hype and publicity, not for measured and scientifically supportable conclusions.
If you care about your audience, and you also care about evidence, you owe it to both to stop, read the article in question, and link to it in your tweet along with your own 140 character sound-bite.
Read it before you tweet it!