The Spaniards don't look on it as badly as the French do the Quebecois accent, but they do seem to think it sounds provincial -- haha, that coming from a people that lisp their way through life!
However, you should bear in mind that Porteno Spanish is not the same as Argentine Spanish -- the accent changes quite a bit and in many regions there's no zh-zhing for the double Ls -- and there's more use of usted in a lot of regions, whereas you barely even hear it in C.F. these days. When you're from Capital, everyone knows it as soon as they open their mouth -- and they get the same kind of looks a New Yorker might get when he's out in the heart of rural Texas "Y'all ain't from around here, are ya?"
The Santiago del Estero accent is quite lilting compared to the Porteno accent, and they speak much slower. The Cordobese is much more neutral, and again, much slower. If you're looking for a place to learn Spanish, Buenos Aires isn't necessarily the ideal, as it has some many of it's own things going on. However, you'll get so used to the speed with which they speak that you shouldn't have too many problems understanding when you travel abroad -- you just have to pay more attention to the y's and ll's then you've been accustomed to. Mendocinos as far as I remember don't use the zh at all, it's been a long time since I talked to one so can't quite recall.