Silverlight 3 运行时版本是3.0.40307.0 
Silverlight 3.0的的控件也增加了很多，加入2.0含有的控件和Toolkit控件和一些新增的SL3控件 
Silverlight 2到Silverlight 3 Beta的变化： 
Ensuring That Your Silverlight 2 Applications Work with the Silverlight 3 Beta ReleaseIntroductionThis topic discusses the changes made to the Silverlight runtime and Silverlight tools between the Microsoft Silverlight 2 and Silverlight 3 Beta. The changes discussed in this article are focused on changes that might cause your older Silverlight-based applications to now fail or behave differently, not on new features/enhancements for this release. 
Note   Corrections/Additions to this document (if any) are listed here. 
Contents: 
· OpenFileDialog.ShowDialog() can now only be opened from a user initiated event 
· HyperlinkButton now navigates the entire window and not just the IFRAME that Silverlight is in 
· Mouse events inside a Popup now give positions relative to the pop-up not the entire application 
· ReadOnlyObservableCollection moved from System.Windows.Controls.Data.dll to System.Windows.dll 
OpenFileDialog.ShowDialog() can now only be opened from a user initiated eventWho Is Affected: All applications. 
Summary 
For security reasons, OpenFileDialog.ShowDialog() may only be called during a user initiated event (MouseLeftButtonDown/Up and KeyDown/Up) or derived user event like clicking a button, checking a checkbox, etc. This brings Silverlight into line with how the other major browsers and plug-ins behave. 
HyperlinkButton now navigates the entire window and not just the IFRAME that Silverlight is inWho Is Affected: Silverlight 2 applications recompiled for Silverlight 3 Beta. 
Summary 
In Silverlight 2, HyperlinkButton behaved inconsistently across browsers. In Internet Explorer, HyperlinkButton will navigate the entire browser not just the current IFrame. 
In other browsers, HyperlinkButton navigates only the current IFrame, which is consistent with HTML behavior. In Silverlight 3 Beta, we've changed the behavior inside Internet Explorer to match the behavior in other browsers. 
Mouse events inside a Popup now give positions relative to the pop-up not the entire applicationWho Is Affected: Silverlight 2 applications recompiled for Silverlight 3 Beta. 
Summary 
Suppose you have an element inside a pop-up that listens to mouse events: 
[xaml]
 
[c#] 
void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e) 
{ 
… e.GetPosition(border) ... 
} 
In Silverlight 2, the coordinates from MouseButtonEventArgs.GetPosition will be relative to the entire Silverlight plug-in, even though the application asked for coordinates relative to the border control (the parameter to GetPosition is supposed to indicate the frame of reference). This has been fixed in Silverlight 3 Beta. 
ReadOnlyObservableCollection moved from System.Windows.Controls.Data.dll to System.Windows.dllWho Is Affected: Silverlight 2 applications recompiled for Silverlight 3 Beta. 
Summary 
This class has been moved into System.Windows.dll so that other APIs in System.Windows.dll can use it. In order to minimize download size impact we've removed some uncommonly used methods. 
Note that this will not affect applications compiled for Silverlight 2. If you use ReadOnlyObservableCollection in Silverlight 2, your .xap file will contain a copy of System.Windows.Controls.Data.dll. When Silverlight 3 Beta runs your .xap, it will use the .xap's copy of System.Windows.Controls.Data.dll and that version of ReadOnlyObservableCollection, not the version that ships in the System.Windows.dll of Silverlight 3 Beta.