countCSSRules.js

 function countCSSRules() {
        var results = '',
        log = '';
        if (!document.styleSheets) {
            return;
        }
        for (var i = 0; i < document.styleSheets.length; i++) {
            countSheet(document.styleSheets[i]);
        }
        function countSheet(sheet) {
            var count = 0, countRules = 0;
            if (sheet && sheet.cssRules) {
                for (var j = 0, l = sheet.cssRules.length; j < l; j++) {
                    if (!sheet.cssRules[j].selectorText) {
                        continue;
                    }
                    count += sheet.cssRules[j].selectorText.split(',').length;
                    
                }
                countRules += sheet.cssRules.length;

                log += '\nFile: ' + (sheet.href ? sheet.href : 'inline <style> tag');
                log += '\nRules: ' + sheet.cssRules.length;
                log += '\nSelectors: ' + count;
                log += '\n--------------------------';
                if (count >= 4096) {
                    results += '\n********************************\nWARNING:\n There are ' + count + ' CSS Selectors in the stylesheet ' + sheet.href + ' - IE will ignore the last ' + (count - 4096) + ' selectors!\n';
                } else if (countRules >= 4096) {
                    results += '\n********************************\nWARNING:\n There are ' + countRules + ' CSS rules in the stylesheet ' + sheet.href + ' - IE will ignore the last ' + (countRules - 4096) + ' rules!\n';
                }
            }
        }
        console.log(log);
        console.log(results);
    };
    countCSSRules();

Added a warning for the rules. Found out that the maximum numer of 4096 counts for rules as well as for selectors in IE7.