Apple's Disk Utility program is a useful tool for managing hard drives and volumes; however, in Snow Leopard, Leopard, and other past versions of OS X, when you would run a drive verification routine it would only access the format structures of the volumes on a drive and check them. For instance, if you have a drive that is partitioned into two volumes, then if you select one of those volumes in Disk Utility and run a Verify Disk routine the program will check the volume's formatting in a routine similar to the following:
If on the other hand you selected the drive itself instead of a specific volume it contains, then Disk Utility would repeat this process for all of the volumes on the drive, checking them sequentially. This behavior was convenient; however, it did leave out the option to check the device-level features such as the health of hidden partitions, the partition tables themselves, and various other low-level features on drives such as boot loaders.
This has changed in Lion, and now Disk Utility will check these device-level details so if you select a drive device in Disk Utility and run the Verify Disk routine, the tool will check the partition list and various boot partitions and files instead of only checking the volumes on the drive.
In addition to checking these various routines, you can now run them on multiple drives or volumes in one run by holding the Command key and selecting the drives and volumes of choice before starting the verification or repair.
While this new feature of Disk Utility is very nice to have, it may still be a good idea to keep a robust drive maintenance tool like Drive Genius, DiskWarrior, TechTool Pro, or DiskTools Pro on your system to fix drive- and format-related problems.