I had my hands on a Alienware 14 laptop for past few days and once I started got back to my Macbook Pro Retina, I started feeling that my Macbook had become too slow. Call it just the switch back from a better laptop to mine, but I wasn't really happy with the way it was performing.
Now mine is a top of the line Macbook Pro that I got last year in August when the new Retina display launched, so hardware wise there isn't much that could be upgraded. I did some studying and also started looking for softwares that could help me improve the performance.
I came across System Lens which a lot of people recommended in forums but I couldn't be happy about it. Also I noticed that the app itself was occupying about 10% system memory, which is ridiculous. Overall the app has a nice UI and it stays in the menu bar, but it did not give me what I wanted. Most other apps also failed on me.
However, I came across this nice little trick. All you need to do is shut your laptop off and plug it in to the wall. After that, hold down the left Shift, Option, Control and the Power button all together for 10 seconds. A indication that this worked was that your laptop should not turn on while doing this. After this, turn on your laptop as normal. This should fix your problems!
This a reset of the System Management Controller which is an intel-only feature. There are several resources online if you are interested in reading about it.
Also, another thing that has helped me is Purging.
Open Terminal (spotlight search is easy way to get there), let the terminal load for a second, type "purge" and hit enter. The computer will seem to slow drastically for about 5 seconds or so, then all returns to normal.
This dumps all the stored memory that is not being used by programs. Sometimes there are memory "leaks" even after you quit a program. Purge the system and free up all that space. You'll be surprised how much faster things will run after this.
Hope this helps.