I've been using the nightlies on Linux the last few weeks and have had very few problems. Much more stable than Firefox right now due to a packaging error by Arch.
Chromium is the development branch's name; official "Google Chrome" releases are just snapshots of this project perhaps with additional branding installed. That's how I understand it, anyway. So yes, I've been using Chromium the whole time.
I think it is worth it. It performs much, much better than even the nightly builds of Firefox. The interface is also exceedingly faster than Firefox's interface (moving tabs around, etc.), and this makes it much more pleasant to use.
I switched because Firefox was crashing incessantly because Arch linked it against an incompatible (newer) version of SQLite. When Chromium crashes, just the tab goes down. This is so nice.
I haven't experienced much crashing though. The only problems I've had were a one-time bug that snuck into the build where it wouldn't special-case your keystrokes in a text box so it would read out shortcuts while you were typing (meaning backspace made the page go back) but this is expected and it was fixed in the next build (which I downloaded immediately, naturally) and problems with Flash.
In the build I'm using now, Flash behavior is erratic; sometimes the buttons will work on YouTube and sometimes they won't. Zoomify's buttons never seem to work. Also, occasionally a video will lose sync with its audio and start playing about five seconds before the audio kicks in. As such, if I want to watch something on YouTube, I often find myself using Firefox to do so. If you're a big YouTube or Flash user you might be too annoyed at this to switch. Otherwise, I heartily recommend it.
I will keep using Chromium (and manual updates if necessary) until Google releases an official beta. I do not why but I trust more in the developers in Chromiun that in Google itself.