For me, it can't replace Firefox. I have a few extensions, or plugins for Firefox that I personally can't live without.
which ones are those Scott?
Well, since you asked.

I use
http://delicious.com/ to store all my bookmarks online. At present, I have over 750 bookmarks saved. Anytime I find something interesting, or want to refer to later, I save. As I save bookmarks I tag them with keywords for easier retrieval later. I use the
delicious addon for Firefox, which adds a couple of simple buttons to store and retrieve my bookmarks. It also allows me to sync bookmarks across 3-4 different computers, so if I save it with one...all computers see the update.
I use
Ubiquity from Mozilla Labs. I'm not sure I can explain that one, but if you are curious, follow the link.
The rest are related to web and html development.
MeasureIt is an addon that allows you to measure elements within the browser. Its handy for me to measure the pixel width/height of images and other layout elements when working on web pages.
Firebug is a web development (analysis) tool. If you do web development, with html and css, its the coolest thing since sliced bread. Especially if you are working with complicated templates like this message board. If you don't, its useless to you.
Web developer is very similar to firebug, and I use it for some of the same reasons. I now prefer firebug.
A short list, no doubt, but those are the ones I use on a daily basis. Its not likely anyone else will find them useful, but there they are nontheless.
What do you use? And by the way, I'm glad some of you checked out Chrome. With a little use, I think you'll like it!
-Scott