I have played with Atlas and it's quite frankly overkill for me. Plus it generated some horrible looking HTML and I like to keep my sites valid XHTML1.1.
In the end, I developed my own little ajax library. It consists of two parts: a javascript implementation of a very limited subset of XPath (to make dealing with XML in a cross-browser fashion slightly easier) and an ajax library that provides objects that allow me access SOAP 1.1 Web Services (I'd use SOAP 1.2 but that uses the application/soap+xml mime-type, and most browsers' XMLHTTPRequest objects refuse to return the result as XML if the returned type isn't text/xml, there's usually workarounds for that but of course they're completely different for each browser).
You can see my library in action at
http://www.ookii.org (the comments and the calendar).