Have noticed that Sigma offers an 18-200 with stabilization. For some reason, it is more in my price range, new. The Nikon 18-200 is not, even used. Never noticed it until I saw it mentioned in a review of another lens. It's not 250mm, but it's half that price, too. I'm getting it.
Good I haven't run right out and bought. As more info comes in, the choice evolves.
I'm sure, once I have bot, I'll find fault with the Sigma, too. BUT, I'll live with it. Besides, the d5100 does RAW. Maybe I'll be able to correct any faults in post.
Right now, to learn, I'm doing walkarounds with a Canon sx1610 point and shoot. Good things and bad things about it, but it does, under limited circumstance, take good pictures. Distance photos have a little softness, and the manual focus feature is a pain to use. What I'm using it for is to learn totally manual shooting. Can't wait to get the d5100.