I caught a great article from Codswallop on PDF writers via Digg today. PDF can be useful for sharing documents with users who don't have Office installed, for archiving, or for when you want to print out something and you suddenly realize that your printer is out of ink.
I don't save files to PDF that often, but when I need to, I've got a couple of specific tools that I use that makes the process really simple.
Microsoft Save as PDF or XPS
This utility lets you save files as PDF from within Office applications. This Office 2007 add-in lets you optimize your saved files for print or online use.
CutePDF
CutePDF comes in both freeware and a commercial versions. The freeware version is free for both personal and commercial use. The commercial version offers a list of great features and is currently priced at around $50.00 US.
If you use PDF a lot, you should also check out Sarah's post: Outlook 2007 Tip: Preview PDFs Automatically.