I'm not sure where I pulled this from, but it's been on my mind a little lately, even though I'm sure I got it a while ago. Unfortunately I don't remember the exact words, but it goes something along the lines of; There's no evil in the world, only lack of good.
It makes sense, there's a lot of things that follow the same sort of rule. Look at darkness - there really isn't such a thing as darkness itself. Darkness doesn't spread, darkness disappears as soon as there is light nearby. You can't make something darker, unless you remove light. Coldness is just a lack of heat, again the only way to make cold is to remove heat.
Also there's a limit on each of these - temperature can only go as low as -273.1 degrees celsius, and I'm pretty sure there's nothing darker than the complete absence of light.
I believe this can be applied to evil as well. Evil, as we know it, is created by lack of good. There's probably a limit on the amount of evil someone has as well (see: Satan), but remember it's not the amount of evil, it's the complete absence of any Goodness
I suppose that's why we can be forgiven, and when we go to heaven, our hearts are filled with 100% good, just like Jesus's heart. Down on earth though, there's probably always a dark, cold corner in our heart that's not filled with good. *sigh*
Update on the website; I had to create my own forum because none of the premade ones (phpbb and minibb) would work on this crappy webserver (sorry webserver, if you're listening). I'm about 70% complete on the forums, and it's ugly. I need an interior decorator or something. Stay tuned.