From their site:
As the release of Silverlight draws near, DevExpress has invested the engineering resources needed to deliver a feature-rich grid control for Silverlight. Not just a "preview" of what is possible with Silverlight, the AgDataGrid Suite was developed to fully exploit the power and flexibility of the platform…
It looks like it will support pretty much everything you’d expect in a DataGrid and more…wicked cool. Congratulations and thank you to DevExpress!!!