Microsoft has released the November CTP of SQL Server 2008. This version has SQL Server backup compression and Intellisense in SQL Server Management Studio among other things.
SQL Server 2008 backup compression typically compresses at about a 5 to 1 ratio (depending on your data), and it is an Enterprise Edition only feature. It is not configurable, it is either on or off. When it is running, you will see some extra CPU pressure due to the compression, but in the testing I have done so far, backups and restores are significantly faster (two to three times faster). The reduced I/O more than makes up for the CPU cost. If you are concerned about the extra CPU pressure, there is a way to control it using Resource Governor (which is a new feature in SQL Server 2008).