I got in a rush once and launched with the canopy unlocked on my Pegasus. It rattled a bit while on the runway, but smoothed out after liftoff. It never tried to lift, so I ignored it until after release. No problem locking it in flight.

Reinforced my use of a checklist. Also made me glad I got a glider with a forward hinged canopy. I know of at least two accidents involving side-hinged canopies, and one instance of the rear canopy on a G-103 blowing open and shattering while on tow with a solo pilot.