Hey, cool trick.
1) Open your home folder, then open your Library folder (~/library)
2) If a folder named "PDF Services" doesn't exist, create a new folder and give it this name (no quotes, of course). If one already exists, go on to step 3.
3) Open (in a new window) your "Applications" folder, and Option-Command-Drag & Drop your Mail application (to create an alias) on to the (new) "PDF Services" folder.
From now on, when you go to "Print..." from any application, you'll see a PDF icon (with an arrowhead) at the bottom of the Print dialog, just to the left of the "Fax" button. Click on this icon and choose Mail from the list. This will generate the PDF and open a new mail message window with the PDF automatically attached.
I used to save PDFs to the desktop and drag them to the Mail icon in the dock, but this saves a few steps. Nifty. Learn somethin' new everyday!