Years ago I decided to keep a maintenance log for all my bikes. I track replacement of chains, tires, adding racks or bike bling, or anything else of note.
It also shows how much I ride a particular bike or, in the case of my Ross, the year I bought it from a neighbor's garage sale. You can see my titles at the top of each page - I called the Ross a "Green/Black Bike".
I can tell that I resurrected the Miyata in 2009. The Miyata also has a new back wheel and freewheel of which I've been increasingly unhappy with, so the added benefit of a log is that I can also monitor that arrangement.
Does anyone else do something similar to this?