I put an example online that will show the current beta version of Ajax.NET Professional. Try the page http://munich.schwarz-interactive.de/default.aspx  with your Windows Mobile 5 device. You will see two alerts, one showing the current time of the web server, the second one will return two properties of an PersonX object in a List<PersonX>. Would be nice to see if we get it running on older Pocket PCs, too.
I hope to release this version on Sunday!
Note: only the default.aspx is currently using the new library.