One of the "little" things that's new in CS4 -- not just in Illustrator, but across the entire Suite -- is something called Adobe Community Help. Even though CS4 isn't shipping as of yet, Adobe has gone live with this new help service. Specifically, you can find the Illustrator CS4 Help here, and the Illustrator CS4 What's New section here.
All aspects of this new help system aren't in place yet -- for example, the ability to comment on the help files isn't available yet, and the links to video content aren't working yet -- those will come when Illustrator CS4 actually starts shipping (no idea on exactly when that will be, but I have to assume it isn't too far off).
I've always lamented at how "unhelpful" the help files for Illustrator are. If you think about it, the help files are being written and developed at the same time the application itself is being written and developed. In reality, that doesn't leave Adobe's technical writing team to do much more than struggle to keep up with changes as they happen, and to figure out how to use the features before they can even use them (even authors such as myself have working beta software to help us tinker and play with features until we "get it" and can find uses for it and to teach real-world applications for how they can be used).
That being said, Adobe's new Community Help is a HUGE step in a new direction for Adobe. Rather than try to write everything themselves, Adobe realizes that there's plenty of other great content out there. And so the Community Help system uses Adobe's files as a base, but Adobe uses Google technology to add other content from the 'net. Even better, Adobe has asked some leaders in the field to be moderators (including yours truly) to continuously add new content and comment on items and to generally make the Help system more Helpful :)
So take it for a spin and see what you think. As time goes on, the system will grow and become even better. And if you have suggestions on how to make it even better, don't be shy - let Adobe know :)