I ran a game at GenCon UK 2007, and am running it again at a Con over this weekend using CJ Carella's Witchraft. I don't see any real issues with the lack of a system mechanic for the "Murphyonic Field"... nothing that can't be overcome with a blend of roleplaying and GM fiat in equal parts.

I did find it harder creating decent game stats for charaters like Mouse, Billy Borden, Thomas Raith, etc even with a copy of the Abomination Codex, but with a degree of flexibility and descriptive text in the character backgrounds, even that wasn't too onerous.