I think there'd be no harm in giving them a try provided you stick to smooth roads.
They are verging on being just a bit too narrow for the rim according to what people say, which might give you snakebite flats if you ride where it's rough, have no suspension, are a heavier rider, or don't unweight the seat when you go over a bump. Make sure you keep them pumped up to full pressure.
The ride isn't that bad, I think. A narrow tire compresses easier. Also, if you ride over big bumps without taking the weight off the saddle, you'll just compress them so far that the rim will pinch a hole in the innertube when it bottoms out on the pavement.
They may not give much benefit over a 28mm wide tire at the speeds which hybrids are used at, because you can only get low and aero on one until you get tired of crouching with bent elbows. You may not be able to go fast enough for air resistance's sake to feel much benefit from them.
You do need a new tube. Even if you get the old ones in there, having all that extra rubber in there will add rolling resistance and take away part of the reason for getting such skinny tires.
Last edited by garage sale GT; 04-23-11 at 08:12 AM.