Of course, I do!
But only on select markets and routes that is
I can never justify spending my hard earned dollars for services that are often priced out to be 10K or so (although I'm slowly realizing the bang out of those RTW fares-somthing to look forward to). The fact is, there are cheaper, smarter ways to pay for travel in premium class, and that's the most important thing.
In any case, intra-Asia premium tickets are often reasonable and offer high value per dollar spent. In addition, QUP/YUP fares in the US can be a good deal as well for last minute travel or on ocassions where the difference between a Y and F seat is only a few hundred dollars.