We need to build an administration portal website to support our client/server application. Since we\'re a .Net shop the obvious traditional way would be to do that in ASP.Net.
There are some downsides with developing a site completely in Flash / Silverlight, but if those downsides won't matter to you or won't have an impact then there is nothing stopping you. Choose whatever tool you think meets your needs more fully. I wouldn't be put off creating a site purely in Silverlight based on the downsides, because it brings a lot more positives to the user experience.