No. I have never flagged a hub. There are certainly ones that I didn't like, or didn't match the subject they were about. But, I don't think it is up to me to say if that person's hub is worth being published here. If I don't like it, I just move on to something I do like, and I don't worry about it.
What I don't like is hubs that are nothing but pictures, with very little or no description. Whats the point of a hub like that? It's almost like the person's only goal is to make as many hubs as possible for count and nothing more.
But, the ones that I did like, were very well done. Those are the people that I also follow. I don't follow people who don't write good informative hubs. And, I'm not that picky.