The ACLT (Afro Caribbean Leukaemia Trust) is a UK bone marrow and blood donation charity and they're the only ones I've seen who've given
a concrete breakdown on the ethnicity of donors in the UK's registry. It's not worldwide, but I think it's fairly safe to extrapolate data from this considering that the bulk of the worldwide registry is from the US, UK, and Germany.
"This equates to just 4.79% of potential bone marrow donors on the BBMR which is administered by the National Blood Service are from the BME (Black and Minority Ethnic) communities."
The take home message is - if you're white, you'll probably find a match. If you're not, you probably won't. And the only way we as a society can fix this situation is to get more people of ALL races onto the worldwide registry. There was
a fantastic article I read recently of an American Olympic hopeful who couldn't find a match, so he single-handedly started up a Nigerian donor registry.
__________________
36/F - 1984 SAA treated with ATG [complete remission until] Oct 08 - burst blood vessels in eyes and low platelets; Jan 09 - AA & hypo-MDS; July 09 - BMT (RIC MUD PSCT) July 10 - 10k for Anthony Nolan (1yr post BMT! 53:48) Sep 10 - Wedding!

I've run 5 marathons now!! (PB 3:30!)