I'm going to remain skeptical.
Net apps are great, but their performance in many areas is unavoidably way below that of native apps. When you can do everything with JS, you can be reasonably speedy if the processing requirements aren't huge and your browser doesn't leak memory too badly. (Dammit, Firefox!)
But when you need to persist data, you have to spawn an ajax query and that 1/10 to 1/4 second (even over a fast network connection) just isn't comparable from the user perspective to hitting a local HD. As local mass storage switches from HD to solid-state over the next couple of years, the difference between native and web apps is going to increase, not decrease.
Besides, half of these things are going to be ad-supported, right? At least in my experience, the performance of most websites has decreased the last 3 years or so as they hit and increasing number of different servers. It's typical for a single page to load content, ads, local javascript, stylesheets, and analytics from 10 or more pages. Each of these connections triggers its own DNS query. Every connection and every DNS lookup has a %age chance of hanging for a few seconds due to network traffic, server load, or what have you - as a result almost 10% of web pages I try to load these days stall for a few seconds. Do you really want that kind of crap going on in the background while you're developing? I don't.
Hah! Just reminded of a most annoying example! Slashdot, for me, loads pretty much instantly. But every time I post and click that "preview" button, there's a five-second wait before the preview actually shows up. That'll be fun, and additional five seconds for every classfile save in my IDE...