hmm, i don'tknow of the EF-S 17-55mm 2.8IS being part of a kit, as it will add about $800 or more onto the body. Was it the 17-85mm IS? that was part of a lens kit, and still was up until the 50D, i believe.
If it is the 17-85, i haven't had very good results with that lens. I have rented one several times, and it is soft over all. Ofcourse everyone has different experiences with lenses, but i would steer clear of this lens, especially if you pay retail for it. Id pay maybe $200 most for this lens
My 28-105mm MKII MACRO was sharper than this lens.