Not at all. The United States Patent and Trademark Office doesn't make it easy to get a patent. Florida patent attorneys like myself work through excruciating details to secure the approval of our clients' patent applications. Therefore, the USPTO is necessarily reluctant to take a patent away once it's been issued.
When a third-party challenges a patent holder's monopoly, the USPTO reviews the case; however, a very small percentage of patents are revoked. And, even those revoked are later reinstated when the patent holder appeals the decision.
I read an article today about the USPTO's decision to tentatively nullify four patents held by Gilead Sciences, which cover a drug that treats AIDS patients (San Jose Mercury News, January 24, 2008). A consumer advocacy group up the coast from Florida (in New York) called the Public Patent Foundation is the third-party challenger in this case, claiming Gilead's patents are invalid, because they had publicly disclosed the technology behind the drug.
This brings up something I consistently counsel Florida patent seekers (and patent seekers everywhere) against. It is vitally important not to publicly disclose your idea--and in fact not to disclose it except under absolute necessity--before filing for a patent. The USPTO can, and certainly will, reject a patent application for an idea already in the public eye.
Now, I doubt that Gilead, having already secured their four patents, will have their patents revoked. (Even the Public Patent Foundation admits the unlikeliness of this.) And, Gilead, which earned $3.1 Billion in sales based on their patents, says they will "vigorously defend each and every claim." With that big a business riding on it, I'm sure they will.