Beachballing is when Mac OS X displays the rainbow cursor. It indicates the main user interface thread is blocked and waiting for the machine to do something. It's typically frustrating :-)
I don't know what Leica's "DMR" sensor is. Aperture 3 supports the M8, M9, X1, and S2. Can't say on the latter one... pretty sure support is there but I don't have the scratch to try. A full list of supported RAW formats is here:
http://www.apple.com/aperture/specs/raw.html