I started this post several months ago and finally got around to examining some of these libraries. So far, I really like the jQuery library, and of course Sarissa. I like the idea of XSL transformations in Javascript, but it doesn't really work that well as far as I can tell. Its possible with jquery and sarissa, but its a little cludgy. With jQuery, you can interact with the DOM in pretty clean manner, so maybe XSLT isn't the best choice for client side.
Prototype looks good too, but I haven't explored it too much.
I think that for my use XML and XSL will stay on the server, and the client side will only use JSON.
Good article on XML, HTML, and JSON:
There are some nice json libraries:
E4X looks interesting too, but of course Microsoft lacks support for this standard:
I'm having a blast with jQuery. I just added tablesorter to PBooks and 1. it was easy and 2. it works really well. I then found this:
which might be the right solution for me. I've been wavering between XML and JSON for updating content, and I think this might clinch the deal for XSL. I don't think I'll be doing many heavy AJAX data downloads, instead downloading all the data in one fell swoop and then perusing it with a method like the tablesorter pager.