Every day, your site will auto update to the latest nightly build. We committed long ago to ensuring that trunk is continuously dogfoodable and quickly fixed in the rare event that something nasty happens, like a fatal error. I have never once experienced loss of content while following trunk. If you follow this blog, consider putting the beta tester plugin on a real site that you use regularly. We must take this small extra risk with our own sites so that we truly see what we’re making before releasing it.
I run the Beta Testing plugin on two sites: my personal blog and another landing page. For low-risk sites, it makes sense, and I'd encourage you all to give it a shot.