I'm tempted to say - if you feel the need to ask this question, then don't run the beta.
I'm running the beta, and have not found anything that would have caused the loss of data, and so far it has been quite stable - BUT - beta software is pre-release and expected to have problems, and it is generally not recommended that you run beta software in situations where down time and/or data loss would be problematic.
In the corporate world, beta testing is done on systems specifically set aside for such purposes (and I'm not talking about the software developers here, I'm talking users), in SOHO it's less common to find separate systems, but the same principles remain - testing should not be done in a manner that would cause the loss of data.
Since you ask - I will also mention this - even with production software the potential for data loss always exists (it is merely heightened with beta software), have you made plans to deal with the possibility?