You are concerned about rising energy costs?
Your HTPC is acting as a home server and therefore not going to sleep inmediately after your movie session is over?
The upcoming MediaPortal release is going to have less impact on your electricity bill: it will feature an energy save mode.
Along with Cool & Quiet or EIST modern CPUs have various sleep modes (C1-C4). Unfortunately the system is contineously taxed by MediaPortal's rendering engine. On a fast HTPC you might barely notice it but using a FullHD skin with tons of nice animations on an older or undervolted PC might cause as much as 30% load just for the screen and information updates.
Pretty much as quite some MP driven HTPC are even running 24/7.
Therefore the often neglected screensaver (mostly used by Plasma owners to prevent Burn-In) got a new option: instead of blanking the screen completely MP can just reduce it's rendering speed down to 5 FPS.
You'll notice that everything on the screen gets slower then - e.g. the scrolling of textboxes.
Of course this will only apply if you do not watch something in fullscreen mode. As soon as you hit any key MP will be back to its original speed - you shouldn't even notice the transition.
As a result MP should use much less CPU cycles allowing the processor to use its power saving features more efficiently.