It's little things about Chrome that I don't like. Like the inability to have multi-row bookmarks in the bookmarks toolbar (easily remedied with an extension in Firefox). Similarly I tried the AdThwart extension to block ads in Chrome - it works but with one annoying quirk: it first loads/displays the ads, and then removes them after the page has hit 100% completion. It's quick but still noticeable on my 768kbps connection. Adblock Plus' functionality (don't load/query the adserver) is way better.
Chrome definitely does appear to have a faster rendering engine; built-in user scripts are nice as well. I use 'Youtube Enhancer' and frankly couldn't live without it; it works in Chrome but some features appear to work properly only in Firefox.
I also recently installed the Opera 10.5 pre-alpha. The integrated mail client is way too easy. I simply click the mail icon on the left-sidebar and BOOM!, I have quick access to my IMAP accounts with handy quick-reply and easy ability to manage contacts. Clicking on an email link loads a new 'Compose Email' tab in a fraction of a second. That feature and responsiveness is something I definitely wish Firefox had. Smooth-scrolling complex webpages (with tons of embedded flash videos and messy tables) also works better. Stability and random pauses don't seem to happen like they do with Firefox.
But I still use Firefox because of certain extensions, user scripts and overall familiarity. I guess it's the one app I use regardless of performance due to usability.
I'd much rather switch to Opera than Chrome, that's for sure.