PAF offers the floppy disk as a location, but you can send the backup to any writeable location of your choice.
Suppose I want to back up my PAF data to my flash drive: Firstly, I should know the drive letter assigned to it. Then click File menu > Backup > click the "Save in" drop down list to select the location, and give the backup a name > Backup > OK
For example, on my own computer with the flash drive as drive I: File > Backup > Save in > I selected "PKBACK#001(I:)" and gave my backup the name "Current genealogy 26Jan2010" > Backup > OK (The quotes are given in the example to define the exact input. They would not really be used.) Checking my flash drive I see a new file called "Current genealogy 26Jan2010.zip"
Backing up to a CD is more difficult, as the process may vary, depending what CD writing software you are using and whether you are using a CDR or CD-RW. The basic process I use is to backup the PAF database to the computer desktop, then RIGHT-click the icon for the backup file and from the pop-up menu selectSend to > DVD RW Drive (E:), and follow the on-screen prompts.
Backing up to email also works well, so long as the backup is not too large to be attached to the email message. Just send a copy of the backup file to yourself as an email attachment. My gmail.com account can handle attachments of up to 10 MB, which is sufficient for my backups. Then I have a backup safely stored and encrypted on Google's servers ... for free, and accessible to me from anywhere on the internet!
I advocate multiple backups and including the date in the name of the backup. Fortunately, it isn't hard these days and storage space is cheap and generally much more reliable than floppy disks.