As you might know there're problems with aspects by using Alfresco. No other repository seems to have such a behavior with aspects but unfortunately Alfresco does not allow to use aspects as it is expected. Alfresco knows about this and planned to solve this with Alfresco 4 but since this problem still persists in Alfresco 4.0.0c643 we expect or better “we are afraid” it will not be resolved in Alfresco 4.
:!: But WeWebU today announced great news :!: WeWebU OpenWorkdesk 3.2 and Zero Install Desktop Integration (ZIDI) 3.2 will support Aspects for Alfresco 3.4 and Alfresco 4. OpenWorkdesk Version 3.2 will be available at 5th of March 2012 and will implement a stable support for retrieving Aspects from Alfresco.
Yes, but mostly it is currently a workaround for Alfresco-CMIS capabilities!
The support of Alfresco Aspect was integrated withe the REST-API of Alfresco and is not defined by CMIS 1.0. But the good thing is that the CMIS 1.1 draft contains a new ability called "Secondary ObjectTypes" which will lead to a better CMIS compliant solution.