1. It should be used either on a separately installed system purely for testing or on a system on which the entire oprating system has been imaged for recovery and all data has been completely backed up.
2. It is very unlikely its installation could be reversed.
3. It is very unlikely it will be upgradable when the final SP1 is released.
A beta gives the chance to try it and identify any problems but will be useless and redundant at the end of testing and the installation will need to be deleted so it should not be installed on a live system.
I know that probably the majority of those reading these forums will be aware of this but it must be stated for those who aren't.