I started with pen and paper in '88 but in '98 switched to dumping a few stats into a csv file, with both maintenance and ride records:

date,bike,accumulated miles,odometer,maintenance performed,date any parts purchased,where purchased,price

and

date,bike,odometer,trip mileage,avg speed,low temperature,high temp,wind direction,wind speed,notes/route/whatever,stoker (if tandem),max speed

I can suck these stats into Excel or any tool that takes a csv and analyze away.