Slick interface, fast rendering, overall I'm impressed but the beta is still lacking in services that I'm accustomed to, so I'm sticking with Opera and its awesome mouse gestures system as my default browser (for now).
Also, oh the irony!
I've also found that it tends to assign websites from the same domain to the same process rather than opening a new one per tab. This is cool for general browsing, but it's idiotic that they apply this also to web applications - I opened 4 different Google Documents and they're all in the same process, so if one crashes I'll lose my work in all of them!
In terms of memory usage, I've found it scales well - it had quite a large footprint with only 4 tabs open, but I upped it up to 12 and it's only marginally bigger. It looks like it'll be quite good for "power-surfers" with dozens of concurrent tabs.
The overall featherweight champion of the world in memory usage has been decided though - the numbers don't lie:
Chrome, with 6 tabs open, 90MB RAM and 125MB virtual memory
Firefox, with 1 tab open, 120MB RAM and 101MB virtual memory
Opera, with 16 tabs open, 57MB RAM, 91MB virtual memory...