For what it is worth, my experience with zooms is decidedly mixed, so I think what everyone says has an element of truth.
On my Minolta x300, the 35-70 kit lens is nothing to write home about - sharp enough but not very contrasty - the 50mm 1.7 prime blows it away.
On my Olympuses, the zuiko 35-70mm F4 I have (which is supposedly a "budget" lens) is incredibly sharp and I find I use it nearly all the time, but the 75-150mm zuiko zoom is only really OK at F8 or above. The 35-70mm zoom certainly matches the 50mm F1.8 and 35mm F2.8 primes, but is obviously a bit slower. The primes have the edge wide open.
On my EOS300v, I have a very early 35-70mm with no manual focus. Again supposed to be a real cheapy, but it is more than acceptable, whereas a 35-105mm USM which is supposed to be a better lens, is only on a par with the 35-70 - certainly no better.
The good thing about kit zooms is that they are cheap. If you get a good one it will be excellent, but none I have are really unusable.