Use One User Account for Snow Leopard and also Lion (Partitioned)
Unfortunately, presently Lion is still in pre - release stage, so I would certainly not regard it to be secure neither reliable (till its formally launched). Also Apple is very own standards for mounting pre - release os to testers/developers claim to install it on a non - essential hard drive in instance there are troubles.
If you intend to examine it out, I would certainly install it on an entirely different hard drive. And also with no essential information.