If the kit lens had a little more reach (like to 70mm), I might not have gotten the Sigma 17-70. I think the images the kit lens can produce are on par with the 17-70 (unless you're a pixel peeper). At this point, I'm planning on keeping both, but the thought has crossed my mind of eventually getting rid of the Sigma and using the money towards one of the Ltd primes (or a 1:1) macro in an effort to lighten the weight of my kit.
For the price, the 50-200 can produce some amazing images for it's price, as well. As a matter of fact, I have my F70-200 up for sale in the marketplace, one of the reasons being that it's so heavy, in comparison to the 50-200 (about 10 oz. difference).
Other than the tele-zoom, I'm not making any rush decisions on what I'm going to do, but I'm going to make it a point to use both the kit and 17-70 over the next few months and save up some money and then I'll go from there.
Heather