Has anyone ever used so many emoticons strung together? *wink*
IMO, the EF-S 17-55mm is the best general purpose zoom for APS-C. But primes will often give better IQ (there are exceptions) and almost always thinner DoF, etc., since f/2.8 is the fastest zoom available.
The IQ from your T1i and a 17-55mm will far exceed what you'd get from a high-end P&S in almost all cases. I do have an S100, but that's only for times when it's just not feasible to bring the dSLR (the S100 fits in a pocket, which is why I have no real interest in a G-series, etc., although the Sony RX-100 is tempting for the larger sensor in the same size chassis).