I believe that there will always be a place for web applications that are simply / quickly encoded and do not need a fancy interface.
For applications that need all the user interface settings, Flash / Silverlight / RIA will continue to evolve to provide more and more rich graphics on the Internet. We also see a similar evolution on the Windows side with WPF, etc.
In both cases, I believe that most applications will continue to be developed using which infrastructure is the fastest to encode, since most applications are internal business LOBs and simply need to be functional.
I would suggest you consider a hybrid approach - mainly use modern technologies (HTML / CSS / Ajax / etc.), but there are some sections of the site on which the user interface can benefit most from it, Silverlight or other Technologies really shine RIA. Thus, you get the best of both worlds, get bling where you need it, but do not increase the risks of the project.
alchemical
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