[hlieberman]

The security patches is certainly a concern (though testing-security does exist, albeit not with the coverage of security-updates from stable). In my experience, testing is quite stable for 95% of packages; I can only think of a few instances in the last decade that testing has really broken my computer in a way that required me to break out my developer skills. More frequently, you'll find packages which can't be installed because they've been dropped from testing due to RC bugs -- but that's not necessarily a bad thing!