You raise some good points, Stan. A lot of this depends on how you want to use your camera.
>If photography would possible grow into a hobby, few people >would be replacing the 1.8 primes but almost everyone would be >stepping up in a higher quality zoom if they wanted a zoom. A >low cost 17-50 2.8 for example...
This isn't true for me. You mention photography growing into a hobby, and I'll readily admit to being nothing more than an amateur hobbyist, but I've been at it for years, semi-seriously. At one time I owned only prime lenses and developed all my own prints. I'm not going to claim to be a great photographer or a really serious photographer, but at the same time I'm not new to this either. That's just some background context for my response.
I've considered getting a 17-55, but have decided against it because I don't think I'd get much use out of it. As a walk-around and travel lens, I'm often going longer than 55mm, and the 17-55 is bigger and heavier than my 18-200. Further, I'm very satisfied with the results I get from the 18-200, even though I know some are critical of the lens. When I want a wider aperture, I've found that my 35, 50, and 85 primes do a good job, they are smaller than a 17-55, and also are more than a stop faster.
For my use, the combination of slow zooms and fast primes fits pretty well. This may not apply to everyone, but my guess is that among people who own DSLRs, more of them approximate my level of commitment to the hobby than yours. When I get serious, I'll take my time and put one of my better lenses on my camera. When I'm not so serious, or just taking my camera with me in case a photo op comes up, I'll go for convenience and versatility. I'm guessing lots of camera owners are like that, and for them the 18-200 is a good lens.
>...Regarding travel lenses, it would be hard to beat a 35mm prime >as a light small, sharp, fast, convenient single lens solution.
I'm out of town this week-end for a work-related trip with some photo opportunities, and I'll be taking my 18-200. Sometimes I take my 35 with me too, because it's pretty easy to carry, but take most of my shots with the 18-200 even then. I agree a 35 is a good travel lens, but my view is that the 18-200 is better. I'm not saying it would be better for you. I'm just saying it works better for me.
Going back to the original question, though, I think we agree. You'll notice that the very first reply in this thread is mine, and I suggested the 35 f1.8 as a good lens to buy while saving up for an 18-200, because it was a lens you'd want to keep and use even after you have an 18-200. So going back to the original question, we're in agreement. Buy a 35 f1.8, and you'll want to keep it as long as you own the camera.