r38659 introduces a new planet texture caching system. If everything is working properly, you probably won't notice anything after updating, apart from slightly faster game load times. However, if you do see any odd behaviors, especially latency when opening up planet screens, visibly distorted planet art, or slower than normal game loads, that's a sign there may be something wrong with the new system. Please report any such issues in this thread.
On lower end machines, particularly laptops with Intel integrated graphics drivers, you may notice performance and stability improvements. In fact, I believe that after r38659, it may be relatively safe to turn off "Simplified Graphics" on most such machines. If you try this, please let me know how the experiment plays out.