I just ran into the same problem, and so I did a google search and ended up in this question. I also thought that this would just display as an xhr request in firebug, as that would be an easy way to track the event. Turns out they use a 1x1 pixel gif for tracking! If you look at the "Network"> "All" tab in Firebug, you will see a GET request similar to this:
https://ssl.google-analytics.com/__utm.gif?utmwv=5.2.4&utms=28&utmn=1818843630&utmhn=dev-marketplace.asos.com&utmt=event&utme=5(my-home*sub-nav-click*blog-posts)&utmcs=UTF-8&utmsr=1920x1080&utmvp=1920x618&utmsc=24-bit&utmul=en-gb&utmje=0&utmfl=11.1%20r102&utmdt=Build%20%23%20Developer%20Live%20Feed%20ASOS%20Marketplace&utmhid=1950484512&utmr=-&utmp=%2Flivefeed%2Fblogposts&utmac=UA-23521416-1&utmcc=__utma%3D159014575.706813547.1328542287.1328542287.1328604985.2%3B%2B__utmz%3D159014575.1328542287.1.1.utmcsr%3D(direct)%7Cutmccn%3D(direct)%7Cutmcmd%3D(none)%3B&utmu=6AAAAAAAAAAAAAAAQ~
These are the parameters sent in the request.
utmac UA-23521416-1 utmcc __utma=159014575.706813547.1328542287.1328542287.1328604985.2;+__utmz=159014575.1328542287.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); utmcs UTF-8 utmdt Build # Developer Live Feed ASOS Marketplace utme 5(my-home*sub-nav-click*blog-posts) utmfl 11.1 r102 utmhid 1950484512 utmhn dev-marketplace.asos.com utmje 0 utmn 1818843630 utmp /livefeed/blogposts utmr - utms 28 utmsc 24-bit utmsr 1920x1080 utmt event utmu 6AAAAAAAAAAAAAAAQ~ utmul en-gb utmvp 1920x618 utmwv 5.2.4
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