To clarify Mokumé-Gane is not a specific metal but a technique, Mokumé can be made with karated gold, fine silver, sterling silver, copper, brass, and many other metals.
I work with this stuff on an almost daily basis and I love it, while I'm not sure as to the capabilities of it for blocks and such it is perfect for accents and decoration (though I would love to see a copper/brass mokume case, not really cost effective to use precious metals on that massive a piece. Pricing wise a 1"x3" piece of silver/copper just this last week from Rio Grande was $101USD)
The part that I love the most is the patterning,using cutting burs, ball burs and a wide variety of other tools you can create intricate designs on the surface of the metal, then you roll it flat to create a level surface that you can then make into jewelry or whatever you want, another interesting pattern is if you take a long rectangle and twist it then cut it down the center you get a nice star pattern(ill see if I can get a photo of this when I'm at the shop).
Here are a few of my own patterns that I've created recently.
Both of these are silver and copper, in the second photo I put a patina on the copper (by the way, a good brown to black patina (depending on how long you leave it on) can be achived using baldwins patina)
For anyone interested in more on mokume you need to buy the book, 'Mokumé-Gane A Comprehensive Study' by a guy named Steve Midgett, this book will tell you how to prepare, fuse and pattern your mokume, however there were so few books printed that they run about $375-425 on amazon (shesh, when they first came out they sold for $30), One of the guest authors is a guy named Bob Coogan one of the kindest gentelmen you will ever meet, he teaches metals at the appalachian center for craft and he taught the guy who taught me, (not to say I don't know Mr. Coogan)
Anyway, if you guys have any interest in this stuff let me know and ill create a seperate post where I can show my stuff.