I know everyone here is game-set-match convinced that web apps are it and that's that. I think that apps involving LOADS of data like youtube, facebook or (my absolute favorite) fuzzwich belong on the web. But I'm really not that into the notion of replacing previously desktop based apps w/ web apps.
I've said this before, but it feels like a camping trip. You can survive, just not comfortably. I used fauxto the other day to edit some images and it was great. But it was only really great b/c it was free and b/c it was there when I needed it. But... I picked on tool to suck a color from one place and put it in another. I was confused for a long time b/c I was so used to the mouse pointer changing to represent eye dropper thing but it was still the arrow. Maybe they're new, and maybe this can be done through a browser but it brought home the feeling that I was on a camping trip carving meat with a swiss army knife. Take gmail, amazing interface, amazing search but how do I sync the contacts w/ my iPhone? I'm sure there is a 3rd party app that does it but you'll still use the desktop crutch.
I think that the tendancy toward web apps is more of a move away from microsoft than toward something better. But ironically you actually don't avoid the x-platform problem b/c browsers are all different.
The thing that's great about web apps is that you get:
1) automatic updates.
2) no install.
3) works from any machine.
4) access to reams of data.
5) collaberation.
But:
1) no iPod.
2) no graphics card.
3) no digital camera.
4) no phone.
5) no clipboard for anything but text.
6) if I want to email my image from fauxto or flickr to someone via gmail I have to download them it upload it. (Nobody ever mentions this elephant in the web 2.0 living room. How do you get data from one web app to another? An un-started startup perhaps?)
7) Half ass interfaces. I really give props to the fauxto guys for pushing the limits but only half ass users like me will ever see it as a worthy replacement for photoshop.
8) No OS integration. I like how Address Book, iPhoto and iCal can talk to Mail.app.
The tack we're taking is having the desktop richness along w/ a web component that allows publishing and sharing of data as well as intrinsic backups. A user can log in from another machine (w/ our app installed) and see all of his data as if he was on his own box. He can also access loads of data that other users have generated and made public. We use Qt for easy x-platform w/ native feel. We don't touch the registry. Users don't even need to be admin to install. The only thing we don't get is auto-updates. But we're taking the firefox tack and having them download in the background and install on the next app boot.
Much of my direction was inspired by a number of Steve Jobs speeches. Once my phone is a computer, when am I gonna need "my apps" on another person's computer? I'll never touch another person's computer. Thus partially negating the need for web apps.