It's not useful as a browser, as none of the UI is there (e.g. you must type well-formed URLs into the URL bar). It is useful for testing v8, the networking stack, the graphics layer, etc. Note in particular that form controls obey my theme, but that we turn off antialiasing and form control metrics are still bit wacky (respectively, to match the way Windows looks and lays out for expected test output).
There's also been a lot of work done on the next pieces (the UI, the multiprocess bits), but the nature of the problem is that you need to get a large amount of code compiling before anything visible works. And some of those internals are gnarly -- what's the Linux analog of condition variables that work both within and cross-process and that can also be select()ed on? -- but if it were easy it'd be a boring job. You can see some of the IPC tests passing on our builders.