Clarifications
uncle sjohie: PDF files have never been safe. They are written in the PostScript language. Lots of nasty things can be written in this language - even viruses. Also, they allow JavaScript contents. Finally, there is at least one virus infecting PDF files and spreading from them (albeit only if you have the full Acrobat - not just the Reader).
Matt Dodds: The exploit is actually in Internet Explorer 7 on Windows XP machines - the Acrobat Reader is just the vector, which has the "nice" added capability of executing embedded URLs automatically. Version 7.x is not vulnerable and you don't need to update non-WinXP machines.
Anonymous Coward: Foxit is "vulnerable" (in the sense that it can be used as an attack vector) too - the only difference is that there you'll have to be convinced to click on an URL in the PDF file, while with Acrobat the malware runs by just opening the PDF file. Other applications (Firefox, Skype, mIRC, Miranda and countless others) can similarly be attack vectors. The root of the problem is in IE7 on WinXP machines. Microsoft has yet to patch that. Once they do, the problem will disappear.