I was recently privileged to see MS BI Architect Donald Farmer demonstrate Project Gemini (now PowerPivot) at SqlBits V.
Basically PowerPivot is Excel on Steroids, enabling you to define datasets as tables on the fly and join them.
Empowering you to manipulate millions of data rows on a desktop pc, it achieves this using the same compression technology used in SQL 2008.
I'll certainly be looking out for this in SQL 2008 R2 / Office 2010.
The best analogy for PowerPivot so far...