While inexpensive for a full frame zoom lens with that range, the 28-200mm f/3.5-5.6 USM was disappointing. Not very sharp, lots of chromatic aberration.
Yesterday I swapped another old lens onto the T1i, the EF 28-135mm f/3.5-5.6 IS USM. While nominally the same aperture range, the better glass and Image Stabilization make a big difference in sharpness.