I used to be of the "jedi disappear, dark siders blow up" mentality. It's sort of a Jedi let the force flow through them, and so are gathered up into the force and continue to live as a part of it. Dark siders, on the other hand, try to control and "store up" the force in a way. Instead of flowing through them, as Yoda says, they grab it and hold onto it. Thus, when they die, rather than continuing to be carried on by the force, there is a sudden release of the force like water bursting from a dam.

But of course, now that "dark siders" are Sith and those patterns don't apply, who knows? I liked my old explanation and have yet to hear a better one (or any one) from Georgie, so I'm just going to close my eyes to the PT and live on in my dream world. That's always the most mature way to deal with things, right?