What does it mean when people talk about "misaligned" hard drives?
This article should clear it up for you. Essentially, it has to do with the way partitions are created and accessed on drives. The way software reads and writes off of a drive can be based off of old standards that new types of drives (SSD as a primary example) or operating systems (win vista or 7) don't necessarily follow. This can cause newly created partitions to be misaligned with the underlying structure of the disk, which creates more read/write cycles and slows performance, and in the case of SSDs, can dramatically reduce their life.