Starting with the 2007 releases, Autodesk included an HDI PDF driver along with AutoCAD and its vertical applications. This was a big selling point since many customers were misled into believing that they wouldn't have to purchase 3rd party PDF writers for use with AutoCAD. Unfortunately, the "DWG to PDF" driver (pdfplot9) has several very limiting factors that make it useless to many if not most AutoCAD users.

1. It does not observe lineweights when using true type fonts.
2. When publishing multiple sheets, entities from any given layout may actually appear on the wrong page in the resulting PDF file(s).
3. The origin and margins are very limiting.

Despite these shortcomings, Autodesk still lists PDF output on their feature checklist, but the customers still have to look for a 3rd party solution.

Workarounds: Several users have reported good luck with various PDF drivers, including Adobe Acrobat, PDF995, Acroplot, Jaws, and many others.

If it's hard to justify the added expense for a feature that AutoCAD is already supposed to include, PDFCreator is a nice Windows PDF driver.

First Appeared: AutoCAD 2007
Status as of 2008: Still reproducible.
Status as of 2009: (unknown - please email with any info)