On OS X Mavericks, why does it always say my memory used is like 99% of my total memory?
The screen grab is from Activity Monitor.
Most of the physical memory is used, if for nothing else, to cache data from the hard drive.

If you had included the right side of the table in the screen grab you would see entries like "File Cache" and "App Memory", etc. which add up to the number for "Memory Used" on the left side.