I was happy to reinstall ubuntu to my old desktop after some time using linux mint. But, huge problem. The screen was so SLOOOOW and so terribly bulky that I was wondering maybe it's time that I add some RAM or use something lighter than Unity or ubuntu or even throw away that old piece of junk. While being tight and not adding RAM, I did install GNOME, but, sigh, it still was horrid. I modified swappiness, I changed themes, I performed autoclean at the terminal, installed preload and still the same sleepy mess. So, after freshly installing trusty tahr, and toying around with the settings, I found out that if I reduced the value for Scale for menu and title bars of the Displays button from the generic 1 to 0.875, things looked a lot more clear and eye-pleasing, and I've noticed a better overall performance. I suppose it was nothing tough, but it really made a huge improvement. Moreover, since I'm not a big fan of the Unity's sidebar, I chose from the Appearance button Behavior tab to Auto-hide the Launcher (on), thus the annoying little thingy only appeared when I wanted it to.
Like I've already said I'm definitely not going fot the Nobel prize, but I hope this easy little hint might help someone.