Since day one I've been using a small spiral bound notebook with tabs to ID the different aircraft. If its a new plane, I'll add a tab for it, then enter some of the specs, such as where/when it was purchased, engine, wingspan and so forth, and date completed. From there, I'll enter any flight info. For example, if I flew 2x that day, the entry would read something like;

June 17, 2011
2 10 minute flights. Weather was mild with slight breeze from southwest. Plane flew well with no problems noted.

If there are any problems I'll give a brief description. Any repairs or modifications made later are also entered when completed. And last I enter anything unusual or different about the flying day.. a new manuver tried or such. Its pretty cool to go back over 8 yrs. of info. and look at the different planes flight times and so forth. Started with the 30.00 HobbyZone Outlaw, and just maidened a 1/3 Paulistinha. What a hoot! But seriously, however you do it, just do it. It'll be good reading when you get a few years down the road.