>But with multiple textboxes on the page with AutoPostBack true that can be a lot of round trips to the server just to be told you're wasting your time. Agreed a panel can greatly reduce the volume sent over the wire - but you are still adding load to the server. If the logic to decide whether a postback can really be acted on can be encapsulated in the client why not put it there?
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>Come to think of it isn't ASP.NET capable of generating a certain amount of data validation code in javascript on the client?

Yes, asp.net can create javascript validation on the client, but it will also validate on the server. William, why not just turn trace on for those events and see exactly what's happening and when?