The rumors of Google building their own browser are true: Google Chrome is the project, and includes a number of interesting features, introduced in a comic by Scott McCloud. At the top of the list is running every tab in its own process, and also running each plug-in in its own process. That will definitely help with limiting the bleeding when web pages misbehave, as well as with diagnosing the bad component.
Interestingly, one of the lead developers is Ben Goodger, who was a big part of Firefox, but Chrome is based on Webkit rather than Gecko. Chrome claims a number of UI innovations, but they seem fairly simple things to me: where the tabs are, how the auto-complete works, and so on.
For web developers, there's a downside: it's one more browser to worry about. Yes, it's based on Webkit, so in theory it will behave like Safari in all the important ways.
The difference between theory and practice: in theory there is no difference, but in practice there is.
Another downside: this will likely only take market share from Firefox, and not help with the Internet Explorer problem at all...