We have started implementing AJAX in a number of applications here at my work. Most of what we have done has been using agents to bring back HTML to change a web page using the .innerHTML property. But today I was thinking that I could just as easily bring back the same information I can get in an @DBLookup. The approach I took is very specialized, but can be expanded to pull back any information you would ever want. The JavaScript is as follows:

var xmlhttp=false;
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
try {
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (E) {
xmlhttp = false;
}
}
@end @*/

if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
  xmlhttp = new XMLHttpRequest();
}

function getContactPhone(username, objID) {
  var obj = document.getElementById(objID);
  xmlhttp.open("GET", "/names.nsf/GetOfficePhone?OpenAgent&username=" + username);
  xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
      obj.value = xmlhttp.responseText;
    }
  }
  xmlhttp.send(null);
}

So I have the onBlur event for the contact field set to getContactPhone(document.forms[0].contact.value,'contact_phone'); so that the contact's phone number is looked up in the Public Address Book whenever the user tabs out of the field. The agent I created, GetOfficePhone, returns the user's phone number I want with 2 print statements:
Print "Content-type: text/plain"
Print doc.OfficePhoneNumber(0)

This technique could definitely be expanded to do full blown @DbColumn and @DBLookup functions.