Lot's of good suggestions here. I do it a very different way that works for me. I used to put them in one big file, but then couldn't distinguish between, for example, the lists of repair locations as far as which product they were for since they had no label on them. When I sold a camper, I had all the booklets and warranty information for everything in the same folder and didn't think about it when I gave the folder to the new buyer. They got the owners manuals for equipment we took with us.
Now,for each major category of owners manuals I set up a binder. [Examples: stereo equipment, major appliances that stay with the house, appliances & equipment that go with me, one for each computer, etc.) I put a large quantity of top loading sheet protectors in each notebook. Then as I'm filing or when I buy a new item, I can slide all the paperwork associated with it into the sheet protector. What I particularly like is that the sheet protectors accommodate odd sizes, diskettes, CDs, booklets, odd pieces of equipment. Receipts can also go in here. By having many extra empty sheet protectors in the binder, there is no barrier to filing. Open the notebook and slide the manuals into the first empty slot.
Label the spine of the binder and keep it where it makes sense to you. For me, the stereo equipment notebook is in the cabinet with the equipment, the computer binder is near the computer, etc.