Hi,
I'm using version 2.2.0.1 at jquery environment, all fine.
Using same configuration I'm trying to upgrade to 2.2.5 b3.
During the load of the page I'm getting error (Firebug console):
userSettings is undefined
..../js/swf/swfupload.js Line 149
Have no idea where to start 
My setting doesn't have any "userSettings", just "var settings"
$(function() {
if (typeof(SWFUpload) === "undefined") {
return;
}
var settings={
flash_url : js/swf/swfupload_fp9.swf",
flash9_url : "js/swf/swfupload_fp9.swf",
.............
...............
};
swfu = new SWFUpload(settings);
});
BTW - I'm using kind of the "Application" demo configuration. Reviewing the the 2.5 beta demo, the swfupload.js of the demo is NOT the same version of 2.5B3 release 
July 13, 2010 - 2:51am
The thing is that initSettings is not getting any parameter, so I have fixed it doing the next:
// In swfupload.js
33| this.settings = {};
34| this.tmp_settings = userSettings; // Add this
35| this.eventQueue = [];
148| SWFUpload.prototype.initSettings = function (userSettings) {
149| userSettings = this.tmp_settings; // Add this
// In swfupload.queue.js
18| SWFUpload.prototype.initSettings = (function (oldInitSettings) {
19| return function (userSettings) {
20| userSettings = this.tmp_settings; // Add this