As a fan of the series, I have to say that I'm really looking forward to seeing Eclipse, particularly because I'm interested in seeing how David Slade - who did an amazing job with 30 Days of Night - applied his sensibilities to Meyer's melodramatic material and Melissa Rosenberg's adaptation of said material.
2) The Twilight Saga is one of the only book/movie franchises that I can think of that is 100% 'niche', but has nevertheless become overwhelmingly successful. The books are not for everyone, and while Meyer might not be the most gifted of writers, she has nonetheless managed to create a story that is captivating and interesting to many.
3) Regarding what 'social' or 'moral' impact the novels might or might not have on future generations of young women, I personally think that such concerns are extremely misguided and, ultimately, baseless and unfounded. Yes, there are certain negative conotations that one could derive from the behavior of the characters - male and female alike - throughout the series, but practically anything
can be skewed to be negative if one is so inclined.