UIWebView: How to tell when part of the HTML is visible?
@property(nonatomic, readonly, retain) UIScrollView *scrollView

NSArray *subViews = [NSArray arrayWithArray:[myWebview subviews]];
UIScrollView *webScroller = (UIScrollView *)[subViews objectAtIndex:0];

UIScrollView *webScrollView = myWebView.scrollView;
webScrollView.delegate = self;

//implement method from delegate..

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    //Scrolled
}

CGPoint offSet = webScrollView.contentOffset;