Good or bad? It depends, I think.
Given all the standartization efforts put in Web technologies it would be natural to expect some kind of baseline reference implementation to emerge, WebKit isn’t a bad choice for that.
To rephrase that — I don’t think that implementation of Web standards is the only field for browser vendors to compete in — so sharing common codebase for HTML rendering is a good idea.
Some people think that browser monopoly can hurt the Web ecosystem and provide “IE6 domination” case as an example. But… there is no browser monopoly on a horizon — that’s only about browser engines — and, as I’ve said already, browsers should not compete in a “best Web standards implementation” but rather in providing best user experience.
Luckily for browser vendors — there’s still a huge gap between Web and so-called “native” applications (and vice-versa of course) — so there’s a lot of work to be done on that side.