ASP.NET 2.0 has some frequently requested client side features, as well.  First, it was way too hard to add client side click handlers in ASP.NET 1.x (using the Attributes collection), so now there is an OnClientClick property that can be used.

Another frequent request was to improve support for client-side Focus.  Several features have been added to address this, including a Page.SetFocus(control) method which works today in the alpha builds of VS2005.  You can also declaratively set the default focus of a form by specifying a DefaultFocus in the <form> tag.  This also supports a DefaultButton property, which will ensure that when the user hits enter, that button is clicked.  I know these features will handle a LOT of frequent questions on several lists and forums I frequent.  Example syntax:

 <form DefaultFocus=“textbox1” DefaultButton="button1" runat=“server”>

You'll also be able to specify an individual control and call its Focus() method to set focus to that control.  With the current build (March 2004 Preview) I'm not having much luck with the <form> and .Focus() techniques, but the Page.SetFocus(control) method has worked since before the PDC03 preview bits.

The validation controls also have a new property, SetFocusOnError (boolean), which will set the focus to the first control on the page that had a validator fail.  This seems to be working currently.