The current silverlight 1.0 beta is about 1.38MB (not the 1MB spoken about by Microsoft).
The 1.1 alpha (which includes a subset of .NET) is 4.24MB!
That’s not big for broadband but let’s not be arrogant and assume everyone has that yet.
In terms of competing with Flash, which it does – no doubt – the issue is really about ease of installation. Flash was first installed on systems with Windows 95/98 were everyone has administrator rights. Installation on Vista will be blocked without administration rights which are not granted by default (even to administrators which must temporarily elevate their rights).
Note that Scott Guthrie demonstrationed is ~20 second install on XP SP2, not Vista with it’s “Cancel or Allow” guardian.
Some people may have forgotton that Click Once gives a web distrbution model for full .NET application and the .NET user Controls can already be hosted in IE.
Microsoft must use Windows/Microsoft Update to push through this technology if they want to see rapid adoption, or a good set of compelling applications – is Major League Baseball (a demo at Mix) really that popular with the rest of the world?