In non-circle charts the mouse-over function should fire all the time when a data point’s X-coordinate matches the current mouse position’s X-coordinate, regardless if the Y-coordinate is matching. This would be a more comfortable user expierence, without the need to aim precisely for a datapoint.
The cursor should only change if the user is really over a column for example. The datapoint should be highlighted in any case. If it is a stacked chart, all matching datapoints should be highlighted.