I am just doing some tests on Analysis Services 2012, ready for my talk on load testing at SqlBits X (http://sqlbits.com/Sessions/Event10/Load_Testing_Analysis_Services)
To quickly test cube processing, I took AdventureWorksDW, scaled up to 180 million rows and did a full cube process. 2008R2 was 4% faster than 2005, but SQL 2012 was some 56% faster than 2005!

Not yet sure as to what is causing the better performance, maybe the default thread settings for processing are much better configured to modern hardware.
The test configuration was:
- AdventureWorksDW scaled to 180 million rows for reseller sales
- Partitioned by Month
- Dell R410 server with 64 GB ram and 24 logical processors across 2 NUMA nodes