We were robbed at gunpoint travelling at night in a Paxeos shuttle from the airport to Granada in July of 08. There were 9 norteamericanos in the Paxeos van, including young children. I no longer travel at night, and would emphasize this rule for travelling in a van full of gringos fresh from the US with all their cash and goodies. I recently heard that several other groups of tourists have been robbed on the same road (Tipitapa cut off) traveling from the airport to Granada at night. Cuidado.
Another reason to stay at Farmstay El Porton Verde that first night in Nicaragua!