JQuery Querystring Parser

jquery.qsParameters.js

(function ( $ ) {
    $.qsParameters = function(str) {
        var qso = {};
        var qs = (str || document.location.search)
   
        // Check for an empty querystring
        if (qs == ""){
            return qso;
        }
        
        // Normalize the querystring
        qs = qs.replace(/(^\?)/,'')
        .replace(/;/g,'&');
        while (qs.indexOf("&&") != -1){
            qs = qs.replace(/&&/g,'&');
        }
        qs = qs.replace(/([\&]+$)/,'');
    
        // Break the querystring into parts
        qs = qs.split("&");
               
        // Build the querystring object
        for (var i=0; i < qs.length; i++){
            var qi = qs[i].split("=");
            qi = $.map(qi, function (n) {return decodeURIComponent(n)});
            if (qso[qi[0]] != undefined){

                // If a key already exists then make this an object
                if (typeof(qso[qi[0]]) == "string"){
                    var temp = qso[qi[0]];
                    if (qi[1] == ""){
                        qi[1] = null;
                    }
                    //console.log("Duplicate key: ["+qi[0]+"]["+qi[1]+"]");
                    qso[qi[0]] = [];
                    qso[qi[0]].push(temp);
                    qso[qi[0]].push(qi[1]);

                }else if (typeof(qso[qi[0]]) == "object"){
                    if (qi[1] == ""){
                        qi[1] = null;
                    }                    
                    //console.log("Duplicate key: ["+qi[0]+"]["+qi[1]+"]");
                    qso[qi[0]].push(qi[1]);
                }
            }else{
                // If no key exists just set it as a string
                if (qi[1] == ""){
                    qi[1] = null;
                }                
                //console.log("New key: ["+qi[0]+"]["+qi[1]+"]");
                qso[qi[0]] = qi[1];
            }
        }
        
        return qso;
    }
}( jQuery ));

I personally don't see the point of making your code dependent on jQuery. You could just release it as a standalone JS library.

Other than that, good job!