I have to agree with Chris. The API for working with Javascript (DOM2) across different browsers isn't all that horrible. Although it will be interesting to see what IE7 brings to the mix. There are many many sites (quirksmode.org one of the best) of people who have run into problems, and solved them. Nearly all of the browser-specific functions have their equal in another browser, and can easily be managed (for the time being).

I also agree that native apps aren't going anywhere. I can forsee a larger discord (think a different digital divide) between how far web-apps will go, and how much further native-apps can go. The maxim "worse is better" still holds true. However, I would also ask those who develop native apps, where is your UI experience going in the future? It's been my observation that the browser UI experience is catching up on the native experience; the native experience hasn't done much to distance itself.