nah, none have been momentary. they've mostly been at lights where i didn't feel like unclipping, but had to stay on the bike for 30 seconds to a minute...i'm often able to keep rolling, but in these occasions, i couldn't, and just used back and forth pressure on the pedals and playing with the front wheel to stay upright. they haven't been pretty, but they keep me upright and in one spot while waiting for the light. i think they'd happen more often if the situation were replicated--being around people i didn't want to fall in front of, so i was trying extra hard. when it's just me, i'll stall a bit, but as soon as balance even wavers slightly, i figure "who am i trying to impress?" and just put a foot down.