Aggregations shouldnt really ever go above 20% - AS can use aggregations from any level so full aggregation will never be needed.
ROLAP dimensions perf has been improved a lot since as2k. They can be used for huge dimensions - millions of members. Query perf will be hit though.
Proactive caching isnt the best thing if you have a non trivial ETL process.
Need 64bit version of products to access > 3Gb of ram.
Partitions
2005:
As a practice one partition should have 2GB or 15 million rows for effective performance. Unnecessary partitioning may degrade you cube performance instead of improving it. Also too many partitions makes it difficult to manage.
Slice property is not necessary after SSAS2000