As I've blogged earlier about Intersoft's WebGrid.NET product, I came across the ASPNetPro magazine article reviewing the product. It was a very positive review that cautioned against the IE6 or higher rendering requirement.
This is not a current concern for our application, and Intersoft says they are developing a version that interops with both IE6 and Firefox. Whether or not that comes to fruition is a risk that anyone implementing the grid has to consider. I don't believe this article is behind their pay-site interface, so I'll let the review speak for itself.