The truth is, the show was popular because most modern women were able to relate to some of the situations the female characters found themselves in.
Sure, the fabulous apartments, expensive shoe collection and cheap laughs and innuendo-filled gags did (at times) take away from the realism of the show but generally, a lot of single career women could relate to the relationship woes featured in the show.
The lasting effect of the series is that now, a lot of females aspire to the "Sex and the City lifestyle" – the great jobs, the great apartments, the glam wardrobe, going out for cocktails etc.