What are the short/long term effects of a hairline skull fracture. 3" in length from lambdoid suture forward toward the temporal bone.

Usually none. In an adult, the type of fracture you describe really has no long-term effects. Short term problems really have to do with any associated intracranial problems (hemorrhages, contusions, etc.). Potential fractures requiring treatment are ones that are exposed through the scalp (open), significantly depressed, ones involving skull sinuses, which can leak csf, or "growing" fractures in young children.