Have participated in numerous sprees for 1yr+. So far so good. have not been scam before and keeping my fingers crossed. =) Normally i will only joined sprees whose organisers have good feedbacks or are regulars in the communities.
I must say the postman in my area is very honest. have not encounter any lost mails thought i opt for normal mails most of the time. I heard some spree-ers encountered lost mails frequently in their area. So for those living in that kind of area, i guess it's best to opt for registered mail.