so if you found a great application that perfectly matched your needs, you wouldn't use it purely because it required installing software on your computer?
Not a good example. Netflix would have chosen Flash probably if it wasn't for a special deal with Microsoft. They traded something in exchange for choosing an inferior solution (inferior in that it requires a download).
The whole point of a collaboration type app, is that you can use it from anywhere - your laptop, desktop, iphone, nokia, netbook, internet cafe, library, wii, etc etc
Requiring a user install some software negates the whole point for me.
I'm also betting against installable software (Silverlight plugins excepted!). You just need to look at Joost's traffic since they went web-based rather than desktop client:
I'm hopefull that over the coming months / years Microsoft manage to get Silverlight out there and available on as many platforms as possible, allowing me to write applications that can take advantage of that reach.
In the meantime the aim is to start building up enough user numbers to create a viable business, I've got very low overheads and no debt so hopefully that can come from the existing Silverlight install base + people who are willing to install it if they think the application will do a job for them.