Debunking the why's:
Myth: The UIs are easier for non-technical people. All you need to know is a web browser.
Fact: It's far easier to make powerful UIs with traditional Windows and Mac components. The UIs are much more consistent on Windows or Mac as well, whereas every web developer has to be clever to figure out how to get reasonable interactivity out of a web browser. All computer users are aware of how to click a different icon to get processing.
Myth: The stuff is accessible from anywhere!
Fact: Sure, if their servers are up. The web is stateless, but unfortunately requires a connection exactly when you need it when you use it as an application. How often have you wanted to get to Gmail and had "Service unavailable" for 10 minutes or more? Using POP with Outlook or Thunderbird means you can get to your email when you need it, and just new email wouldn't arrive while the connection is down.
Myth: More reliable! No more having to back up your hard drive?
Fact: If you believe this, you haven't tried using any of these. You obviously never have lost something you've typed for hours into a Gmail or Blogger window and then had Gmail crash and lose your work. Or you've never submitted something, had a problem with the web server, then try to go back to the last webform with the back button and see all of your typing lost.
The bottom line is, by accepting Web 2.0, we're back to the mainframe days, except with with less reliability. Did you know that a <1% failure rate is considered acceptable to a lot of these web companies? Can you imagine of 1% of Word users were losing their work lately, what the outcry to Microsoft would be?
Thanks, I'll take my desktop apps. I wouldn't mind having web-delivered applications, like Avalon/XAML or Java Webstart promise. I don't mind them as long as they can use IsolatedStorage to store stuff on my local disk, then back it up to the server later. What I really don't need is waiting on a less reliable central server than an AS/400 to write a Word document just so someone can put ads in front of me.
PS - I just lost a big section of this message because Blogger didn't properly interpret the less than sign, thus trying to make it into an HTML tag. These web apps are for the birds.