That's not correct, at least with jQuery 1.2.1 on FF 2. this.namespaceURI will give you an attribute error, because this is not a DOM node. It's a jQuery wrapper. The get method unwraps it.
Ah. Well, if this is a jQuery object, then this.get(0) should work as well.
The docs explicitly say about each (http://docs.jquery.com/Core/each) that “every time the passed-in function is executed (which is once for every element matched) the this keyword points to the specific DOM element” though, and it has in practice behaved that way for me. Very odd that you get different behaviour. *headscratch*