What do you know about Musicjapan?

Sorry I can't help with Music Japan as I have never ordered from them. I have, however, ordered many times from Mundo and used from Tokyo Music. I have also ordered from CD Japan. I can recommend Ray Mizutani at Mundo, about 10 transactions all very smooth with excellent communication. Shipping from Japan is a killer though. EMS being most expensive but fastest and most reliable (trackable and insurable). Airmail and registered airmail are next then SAL (surface air lifted) which is flown to USA then ground to destination. There's seamail of course but you'll forget you ordered before the package arrives. I hope this helps some.
BTW: CD Universe carries many Japanese CDS. If they have what you want it's much easier and in the long run cheaper. Ebay usually has a nice selection of Japanese CDs.
But, unfortunately, some CDs still have to be ordered directly from Japan

I ordered two classical discs from musicjapan on Amazon Uk in July 2006, of Richter playing Bartok, Prokofiev, Beethoven and Mozart concertos, on Toshiba/EMI 24 bit remastered CDs. They are simply gorgeous, took 9 days to get to Liverpool UK from Japan, beautifully packed, at a total cost of around £9 sterling. Go for it!

Forgot to mention Jpophelp in Canada.