High Memory usage is not a bad thing. See this article for that: http://www.howtogeek.com/128130/htg-explains-why-its-good-that-your-computers-ram-is-full/
Even Linux, which is more effecient at managing computer usage, has the same "problem": https://atomicorp.com/company/blogs/259-why-does-linux-use-so-much-memory.html
Finally, Mac OS X also does this: http://apple.stackexchange.com/questions/106171/mavericks-unusually-high-ram-usage
All that means is that your computer is using the RAM effectively to quickly open programs, etc. RAM is more power effecient that using a hard drive, because a hard drive is super slow, and the RAM already has the energy.
The cached amount of memory increases because as more programs are opened and started automatically, more cached data is stored, which allows the programs to be opened and started earlier. Without the cached data being stored and that RAM being used, the RAM is "wasted" and that extra few gigabytes is never used. Obviously, you want at least a gigabyte of breathing room, but anything over that is not used.
All in all, don't be scared of high RAM usage as long as you aren't using all of it (i.e. 11.5/12 GB). Generally, Windows knows how to use it.
If all the three major operating systems used that much RAM with only a few programs open for no purpose, it's gotta have some usage that's good, right?