This picture cropped up from a MacBook user claiming that it's thermal grease that leaked onto his RAM strips.
...the thermal grease applied to the internal components has leached into the RAM slots on my motherboard and have 'soiled' the DIMM's with thermal grease.
Apple notebook users get anxious over pictures like this because of the whole thermal grease over-application fiasco that plagued the MacBook Pro back in May 2006.
It turns out that the compound is actually a non-conductive, lithium grease that's applied to ease the installation of RAM chips and it's totally harmless. Some claim that the grease was added because MacBook RAM slots are slightly too thin for the chips.