I really didn't read through all of the responses, but here's my 2c as someone coming in from both sides (and mostly concentrating on web apps since 2002)
It depends
You can't just blindly decide "everything should be and will be web based". Nor can you say the opposite. It really depends on the nature of your application, what it is intended for and what kind of tasks it needs to perform.
Having said that, a good blend of both worlds can be achieved whereby you can have "thin-clients" (as I call them) that are essentially desktop-based apps get their data via a web service of some kind (caching wherever necessary) and also have a website sourcing data from the same service.
This allows you to have a very robust and powerful application to which people have access through either web or desktop. For example a sales rep would have the desktop app at work, but if he needs to check something on the road (or input data) he can use a straightforward-no-frills web app. This then affords him the ease-of-use of just connecting to any client's firewalled intranet (that has internet access) and gets him access to his company data.
That can, in turn, be turned into a smartphone application as well. Possibilities are endless.
However, like I said, this should be viewed on a case-to-case basis. If there's no reason for a desktop app, go web app. With local bandwidth being unlimited with some hosts and some ADSL connections these days, it's quite affordable and also much safer and less taxing on internal systems (you don't need your own servers/backup power etc, basically just a router connecting the office to the internet)
Pro's and con's exist with both, and most problems can be solved in both. Personally I think a symbiotic existence between web and desktop is what is needed (not always required, but still need to be thought of carefully) and to push forward into the future