Anybody out there still believing in Mac "invulnerability" might pause to consider this which has been widely reported over the last couple of days by the BBC and, especially, in the New York Times which has itself been subjected to some serious attacks for a while.
Check your App Store / Software Updates for Apple's latest system fix offered yesterday evening.
If you read Rich Mogull's article as Mark suggests, do read the comments too. In the article he talks about completely removing Java from your Mac (which may be fine for most people) but doesn't make it clear that the vulnerability doesn't seem to apply to using programs that require Java (like DreamWeaver as mentioned in the comments) but only to the Java plugin in browsers and hopefully we all disabled those on Euan's advice long ago!
Macworld UK published this summary of Java and other current malware issues yesterday, 14th March, with good links and instructions for dealing with threats where possible. For members unsure what the issues are this article may clarify matters: