[whpalmer4]

Yes, it's normal -- OmniFocus just keeps writing backup files, and nothing deletes them. Each backup is completely independent, so you can safely throw away any that you don't want. If you have Time Machine or Time Capsule backing up your disk, you can probably throw away all but the most recent handful and still be able to consult an older backup if the need arises.

There are some preference settings in OmniFocus (in the General pane) which control the backup frequency. You always get at least 1 per day, optionally 2, and optionally another one each time you quit the program. That last checkbox can get you quite a few backups if you aren't one who leaves the program open around the clock!