I've been playing around with the idea of putting some 19c tires on my bike, not for speed, but just curious how it rides like. Currently I'm using a pair of Panaracer 23c. I'm fairly light weight so I'm not too worried about getting flats with 19c, but just how practical is it to run such a skinny tire on city roads?
IMO, there is no 'real' argument why not. the advantage of less drag is clear. the tires are normally used for time trials for that reason. i'm sure you would notice a difference from your Panaracer, even if it's already a 23c. handling, i'm sure you'll get the same handling. cornering isn't going to be so much about size, as it is about the rubber compound and sidewall. depending on what model Panaracer, i'm sure a 19c is going to be more of a race tire, therefore handle better than a commuting tire.
the downsides are probably clear. those high pressures (up to 220psi for most 19c's) are not very comfortable. especially on city streets. the puncture resistance is for sure minimal. these tires are designed to be light, so things like carbon and kevlar aren't really options. although i can't say no one is doing it. if they are please let me know who. i wouldn't mind giving them a try.
i've recently switched to the Michelin Carbon's (700 x 23c). i love 'em. they're a bit heavy at 270g but they are very comfortable with ample puncture resistance.
i switched after i got sick of the drag from my Armadillo's. mind you, besides weight and rolling resistance, you can't do better for daily commuting and puncture resistance than the Armadillo IMO.