Updated: Finally wrote that Internet Explorer vs. Firefox/Gecko post.
So we built a browser (skin) last year. Its based on IE, and we shipped the first version in the summer, which for arcane, not really important reasons, was version 1.1. As a part of AIM Triton and the AOL Suite, we also just shipped version 1.2 in December.
I'll explain in some detail in a future post why we chose IE - though we've generally recieved pretty positive reviews for an AOL browser since it GM'ed in July, that we chose to bet on IE has been probably the only consistent and nagging ding. It bears some exploration (no pun intended :))
Interestingly, version 1.1 was built in HTML. That is, the chrome itself was actually just DHTML content (no, not AJAX - DHTML; there is a difference you know). In version 1.2, we rebuilt the whole thing with Boxely, which I'll also be discussing in some depth. This made it a lot easier to do some fun stuff. Nothing you haven't seen before (in principle) but... try it.
We've had, over the last year, quite a bit of mileage in building desktop applications with markup and script. We've got probably a good 10million+ uniques running desktop apps built this way, and there have been some pros and cons - though ultimately, it IS how apps will be built.
In the meantime, I think we're among the bold few attempting to use script for Programming in the Large, as they say, at least for desktop apps. There are pros, and there are cons. More on that soon.