Generally when mine feel flat, I will ride it for a few more weeks out of laziness and then get around to checking them when I see someone else check theirs at a servo on the way home from work or something....
Drmsby Middleton DC Racing
Extreme Motorsports
M2R
Castrol
ColourSmart Chroming
Hi Side Leathers
Teknic
Sidi
DID Racing Chain
Goodridge
the night before i go for a big ride, i check the pressures, otherwise i'll check em in the morning on the way out at the nearest servo wth a reliable tyre pressure gauge so the tyres dont get too warm.
before a long ride (interstate). or about once every 2 weeks or so, unless it feels ordinary..i too use to keep my own tyre pressure gauge under the seat too, but ive lost it sumwhere...