I noticed the same thing on my girlfriends CR-48, twitter wont scroll properly (studders) and everything else hangs a bit. She filed a bug report with google chrome os support, but I suspect twitter is doing a lot of heavy stuff in the background.
I've noticed the same thing on mine. It seems like the site is only functional when you first load it. After new tweets start rolling in, it becomes worse and worse. I don't think it's the fault of the CR-48, I think we're just seeing the effects worse on this hardware.
Same thing here. It's not ChromeOS-related? I note the same problem in Chromium.
I believe the scrolling issues are tied to their use of position: fixed for the sidebar where that DIV has its own internally scrollable frame via overflow: scroll. The combination of those two are taxing on the browser's overall layout system which causes a dramatic slowdown on less powerful machines. Heck, it's even a little sluggish on my iMac.
I'll second this. It's by far the worst performing website/app I use on a regular basis on my Cr-48.