at the risk of inciting a riot on the internet...I have an opinion.
I work in a warehouse for an industrial lighting manufacturer/distributor. Street lights, High bay lights, Parkades and parking lots etc...
COB is definitely the "thing" it seems now, however after speaking with a few sales reps I'm not going to be rushing out and buying one any time soon.
The guy who sells these things, whose pay check comes from them selling, told me (today) COB have a higher burn out rate and run much hotter.
The bigger the cluster, the higher the heat/burn out rate.