Always save your SHSH blobs anyway.
It's a beta for developers not for the public. It'll be a little unstable at this stage (day frickin 1). Probably best to wait.
If you do get a developer to give you beta access know that you'll need to upgrade along with the betas as these expire. So you'll need to get beta 2 when that comes out and so on.
Downgrade I would think would be possible and fine (so long as you have your SHSH). The only problem may be if there is a later baseband in iOS6 it may cause problems when downgrading.
Probably best to wait a little while.