Snow Leopard and Leopard users are familiar with Time Machine and may have used a Time Machine backup to recover from a failed startup drive. I, for one, have done so on more than one occasion.
A new Time Machine feature is available today in Lion. You can now use a previous Time Machine disk with a new computer and inherit the entire backup history of the older machine. Now Mac users can theoretically maintain a continuous set of backups across multiple computers' lifetimes, which does a lot towards making sure that your old data never gets lost.
You can find out more in this MacWorld story that spells out the process in detail.