I updated my beta opt-in settings this weekend after installing the latest OS X updates on my mid-2011 27" iMac. Upon checking, the Beta Opt-in Application did not correctly identify the primary video card. Instead of the AMD HD 6970M with 2GB GDDR5 it instead saw the HD 3000. It did, however, correctly identify the amount of video memory.
Also, of less importance, it incorrectly tested bandwidth drastically below normal tests. Speedtest.net result is usually 55-60 Mbps, Beta Opt-in was 4 Mbps.
27" mid-2011 iMac running Mac OS X 10.8.5
2nd gen Core i7-2600 at 3.4GHz
AMD HD 6970M with 2GB of GDDR5