At 504 miles (407 since acquisition back in November), I decided that the gas indicator was showing low enough to make it wise to fill the tank. So I did. This fill was for eight-and-a-third gallons, yielding an experienced MPG of 49 in mixed city/highway driving. Pretty good, given that the EPA figures were 45 highway and 48 city.
The book wasn't clear on what I should fill with - it said "Unleaded premium 87 octane (91 Research Octane Number)". Unfortunately, that 87 is not clear as to whether it should be interpreted as Motor Octane Number or US/Canada Pump Octane Number - and when I filled up, I had no idea what "R+M/2" method meant - so I played it safe and filled with Premium, labelled at the pump as 92. When I got home, I did some checking, and assuming that the Wikipedia article on Octane Rating is accurate, the 87 cited in the book is most likely the Pump Octane Number, and I can probably fill with regular. If it turns out to be the Motor Octane Number, I can still use Plus, instead of premium, so I'll be cutting my gas costs even more (as the Camry was tuned for a lean mixture, and was always filled with Premium).