SQL 2008 Compression and Table Partitioning are not to be underestimated. They have allowed us to easily justify going to Enterprise Edition instead of Standard Edition when we upgrade from SQL 2000.
Our two largest databases BUDGET_HOURLY and BUDGET have been reduced in space used for the data files (mdf files) from 531 Meg to 106 Meg and 239 Meg to 44 Meg. In the BUDGET_HOURLY database all tables were compressed and in BUDGET database we compressed only tables with more than 10 million rows. The table partitioning greatly improved nightly index rebuild times on the largest tables, and the applications is running significantly faster.
SQL Server 2008 is running as a virtual machine under Hiper-V, but on a faster box than the SQL 2000 so comparing run times gets complicated. Suffice to say, we are very happy with the results of moving to SQL 2008 Enterprise on a virtual machine. We really did not think we could justify Enterprise Edition until we did the testing, but we had the machine and we had the time, and the results far exceeded our expectations.