If you follow the pattern from the earlier books, the Dark One seems to always be focusing his personal efforts towards a Major Project. First it was to lock the seasons in winter. When the Green Man put a stop to that, the Dark One shifted gears and stopped the seasons in the eternal summer. It took the heroes awhile, but they eventually fixed things with the Bowl of the Winds. With the seasons moving naturally on to spring now, it seems likely that the Dark One has begun to focus his efforts somewhere else, and it stands to reason that the next Project should be even better than those before due to his increased freedom. My guess is that his new Major Project is the ghost phonomenon.

Although it seems fairly innocuous so far, the seasons locking weren't a big deal at first either, so we might just be seeing the tip of the iceberg here. Who knows, by the middle of next book, there could be all sorts of specral sightings from Saldea to Shara. If Rand decides to do something about it, I just hope he remembers the perils associated with "crossing the streams" that he learned about in Shadar Logoth with his and Moridin's balefire bolts.