Bugs and Wish List
MouseOvers shouldn't change the colour of a selected row. But in order to conditionally check to see whether or not selected items are highlighted or not, you would need to set up an array/collection of selected rows..which leads me on to the first item on the wishlist (which I will get started on as soon as time permits :)
Use an array or collection to store the rowIndices of selected items and expose this so that the array can then be passed on and used e.g. grouping records. I've done this with an IE only grid, but I'm a lot better with vbscript than jscript. Have a look at the coolGrid on http://www.stedy.com for some inspiration.
Paging: It would be great if you could store a large number of records in jscript array and page through them without having to refresh the page.
TreeTable: This is my pet project at the moment. If your datasource contains records which have a child/parent relationship, it's nice to be able to display them as a TreeTable. Additional functionality like dragging and dropping children from one group to another is my current goal, but it's a tricky little sucker :)
One interesting feature I've added to my own grids has been the addition of tabs which set the css display property of predefined groups of columns (using COLGROUP) on or off. This is particularly useful when you have a large number of columns and want to avoid horizontal scrolling.