I use a different approach, but I use a computer as well. I have a spreadsheet based hardware database that I started in 1992. Here's the why. I needed a bolt so I went to a local (now out of business) Mustang Store and asked - "I need the bolt that holds the clutch return spring bracket to the brake pedal support on a 66 Mustang." The counter guys had absolutely no idea what I was talking about, no way to find it, and, as this didn't involve me spending big bucks in their shop, didn't care. I made up my mind that if they didn't know, I would find out - and document it. I've been involved with databases since 1965 in engineering, procurement, inventory, manufacturing, reliability and logistics. I used my experience to do "stuff". Oh, the bolt is 43490-S8, 5/16-18X3/4 hex hd with a split ring lockwasher (Osborn AM0005 pg15, AMK Fasteners pg34).
The database has over 9200 entries taken from the Jim Osborn Assembly Manuals, the Ford Car Parts manual, the AMK Products Guide To Ford Fasteners, the two Ford Standard and Utility Parts Catalog, TSBs, and personal observations of my and others cars. If a question arises on a certain car's area, say an electrical question, I can sort my file and see what references I've accumulated on that subject. I also have a spreadsheet listing based on topics from Mustang related magazines that I want on restorations and photos. Same concept, sort by subject and pull the magazine.
And as Jeff states - memory is good too.
Jim
Oh, and the free time thing - I ride my bike five to ten miles a day (weather permitting and not on a NFL game day) to keep my doctor happy; design and build furniture (my own); grow some crops (kiwi, avocado, tomatoes, jalapenos etc); and even dabbeled in some creative writing (SF).
Jim