I've known a few people to do this personally, and I've seen it a few times on threads. It's very uncommon, but it's been done.
Didn't Mike Paletta say he lit his tank for a few hours a day with one of these and then the rest of the day kept it lit with T5s or LEDs? It sounds like (
from this article) he learned about it from Sanjay as well.
I've seen some people do all-iwasaki, though most people can't stand light that bright, and prefer to do 4-6 hours of that and then a normal 10-14 hour light cycle with supplemental blue/colored T5s or LEDs. It's almost the same as anyone who did solatubes to light their tank with sunlight, then they had to supplement heavily with blues/colors to get more than just brown out of their light.
That being said, 10k is an excellent growth light, but also has some of the best coloration from corals I've ever seen. It makes the tank look like snorkeling-depth water, which doesn't have the blue/purple that everyone who frequents RC expects, but under 10k XM 250w my corals glowed colors that I haven't seen out of any other bulb.
That's the interesting/tough part with halide bulbs, is that there is no one perfect bulb, and they all have their tradeoffs. 6500 iwasaki for growth (and probably some colors, though I don't have personal experience), 10k XM for growth and glowing purple, red, and green popping out of the corals, 10k Reeflux making any blue absolutely pop out of the corals, and 20k radiums, providing overall colorful spectrum and deep colors in many/most corals.
When I went LED on my new nanocube, I made sure to get a kit that I could customize the specific LEDs, in case I wanted to try to replicate a specific bulb's spectrum, or mix and match different spectrum qualities of different bulbs. Though I don't think I'll ever get the growth/efficiency of the iwasaki, because I think it's just on a different planet than any of the LEDs available.
so I didn't get it. It's more like i-wassa-ki in japanese (i like irene et ssa like samuel 
