Hi, 

The IGGridView actually derives from UIScrollView, and as such it's delegate derives from UIScrollViewDelegate. This means that you get all of the base class logic as well, which in the case of MonoTouch, means that you get the scroll events: 

http://iosapi.xamarin.com/?link=T%3aMonoTouch.UIKit.UIScrollView%2fE

You can read about the order of events and what triggers them in this article, in the "Event Sequence" section:

http://iosapi.xamarin.com/?link=T%3aMonoTouch.UIKit.UIScrollView

As for detecting if a cell is in view, you can use the following code:

IGGridViewCell cell = _gridView.ResolveCellForPath (new IGCellPath(0,0,0)) as IGGridViewCell;
            if(cell != null)
            {
                // Cell is Visible
            }

Hope this helps, 

-SteveZ