This is for talking about Yosemite. If you have individual issues, please make new threads for those particular issues for faster support and response.
You shouldn't be concerned with what any RAM usage utilities say. OS X is very smart about memory usage. OS X takes free memory, and if possible it fills it up with things that it caches to increase speed. In other words, OS X takes free memory and makes it work for you. The only thing that you should be concerned about is if performance has degraded. So far most users have told me that performance has increased using Yosemite.Not so much a problem but a general observation: it appears a memory hog.