Yahoo have gone and published their
UI Design Pattern Library online to developers. It can all be
downloaded as a series of .js files similar to how AJAX libraries are being distributed here. One of their Senior Web Developers discusses what
how they grade the browsers that are supported and then the
table to illustrate this grading. It's quite an interesting way to approach browser support and accessibility.
I think the Design patterns are very useful to make sure you aren't reinventing the wheel and keep to user experiences that people are familiar with in common web sites such as Yahoo, Google, Amazon etc.
Interestingly they've published a 'connection manager' which utilises the XMLHttpRequest object, so is basically their own AJAX library.
I wonder whether Google will follow suit with this and publish their own libraries for everyone to use as well.