BETA software is BETA software, and as Neil found out (sadly, the hard way), most BETA releases are unstable in some shape or form, though dependant on the program, the way you use it, or the platform you are using it on, you might not see any of this.
DO NOT download and install BETA software of any incarnation if you are not computer savvy or are not prepared for crashes, glitches and the odd reformat.
One thing that really irks me about MS is the way they push their BETA's (Live and WMP 11 for example) when the vast majority of their audience do not know how to get the programs off their system if they develop issues.
Firefox issues as statement with their BETAs advising only 'web application developers and the testing community' to use BETA builds. Serves as a good reminder for what we are getting ourselves into when installing tht 'new version'.
I have the Alpha of Firefox 3.0 at home, it's codename is 'minefield' for a good reason!

Thanks,
Sarah