If you want a bleeding-edge WebKit development tool, sometimes even more bleeding-edge than Chrome Canary/Chromium build, try out WebKit Nightly. It just swap out Safari's WebKit for Nightly WebKit while the whole Safari experience remains the same. Since the whole inspector stuff was done completely in HTML/JavaScript, you get a more up-to-date development tools with it too.

About your other points.

>A real omnibar/awesomebar

I've found Chrome's Omnibar to be very annoying, to be honest. The last version I tried (probably Chrome 14) still couldn't do substring searching for titles or maybe even URLs. Pressing control for navigation (standard Emacs C-n, C-p stuff) change the ordering of navigation items. I've found it to be very much unpredictable and is one of my main reason of not using Chrome as a primary browser.

Firefox's AwesomeBar is awesome, though, only if I could navigate using C-n C-p.

>Syncing

Xmarks[1] works beautifully across browsers and platforms. I've used it to sync between Safari, Firefox and Chrome without any problems.

>Favicons

Have you tried out Glims[2]?

[1]: http://www.xmarks.com/ [2]: http://wiki.machangout.com/howdoi/glims-development-build