A bloody show has always been the start of labour for me, DD was born about 48 hrs later (first baby, long labour), DS was born within about 6 hours.

I've heard the same thing though - if it is purely mucusy without staining or streaks of blood, it usually doesn't mean much. If it is stained or streaked with blood then usually that would mean labour isn't far away (TMI...with DS there was that much blood it was like a period, I actually called my ob because I was a bit freaked out, started having contractions within the hour).