Please note that Rust is very alpha alpha alpha at the moment. Syntax evolves constantly. Several concepts don't even exist yet, and many are present only in half-formed nascent states.
The bottom line is that if you're interested in writing applications using Rust, you should really hold off until 0.4 or so (I'd say give it three months), both to give them time to implement all the missing pieces and then to refactor the Rust compiler to use those pieces, thereby shaking out the bugs and annoyances.
But if you're interested in helping out on writing the compiler itself, or proof-of-concept libraries, definitely consider pitching in. The devs greatly appreciate volunteer contributions.
I guess it depends on what you mean by "ready". For instance, Go 1.0 was released just last week, but people have been building useful things with it for a long time now. I suppose it depends on how much instability you're willing to put up with in order to use the shiny new thing.
As someone who follows the project closely, I do think that almost all of the core concepts will be present by 0.4 or 0.5 at the latest (fingers crossed), which would probably be the best time for eager early adopters to dive in. Also consider that Mozilla will be using Rust for experimental prototype browser engine implementations soon, likely even before 0.3 is released.
But if you're looking for some semblance of stability, I'm not sure what advice I can give beyond "wait for 1.0"--which has no definite timeframe. The Rust devs don't even schedule minor releases more than two in advance, so Rust might jump directly from 0.4 to 1.0, or from 0.9 to 1.0, or from 0.367 to 1.0. But don't worry, when they do make the jump, I'm sure you'll hear about it on HN. :P
If you'd prefer to track the project milestones yourself, check out the Github issues page[1] and browse the currently scheduled milestones from the dropdown in the left column.
This is actually really cool in that it occupies a space between Haskell and Python. It seems excessively verbose at the moment but hopefully that will sort itself out in the end.
The bottom line is that if you're interested in writing applications using Rust, you should really hold off until 0.4 or so (I'd say give it three months), both to give them time to implement all the missing pieces and then to refactor the Rust compiler to use those pieces, thereby shaking out the bugs and annoyances.
But if you're interested in helping out on writing the compiler itself, or proof-of-concept libraries, definitely consider pitching in. The devs greatly appreciate volunteer contributions.