Went with a friend last week of August 2008 for a short weekend trip. Shanghai to Xiamen flights can be cheap, so check regularly. Regular buses from Xiamen to Yongding county; takes three to four hours. Haggle with the local drivers for a private coach to see several tulou locations.
The best tulou clusters are in Chuxi - quite far (almost close to the border of Guangdong) but it offers the best view from the nearby hill. The family in Yanxianglou (Mr. Su) are extremely friendly.