I freezed / crashed recently, playing the most recent Regrowth pack (7.4) with this mod added in, alongside Optifine and the GLSL shader mod. Removing this mod seems to have removed the problem.
Freeze and then crash occurred after entering Witchery's Spirit World. Minecraft's CPU usage went from the usual cruising of less than 40% to maxing out all four cores. Here's a crash log.