charlien
There are indications in these forums that many people are using SME8beta releases in production situations and I do not hear people complaining greatly. Newer motherboards require Centos5.x support and users require php5 & mysql5 which are there by default in SME8bx.
Officially SME8beta6 is not recommended for production use, but you are the person to make the judgement call whether to use it or not. I personally do not see any serious risk in using SME8b6, as the code base appears quite stable as is.
You should assess if any add on contribs you need to use will run OK. See the main wiki page for links to Q&A documents re SME8.
I am sure the developers have been using SME8 for over a couple of years now, any small issues that arise they quickly fix.
Re doing routine upgrades, you should test new upgrade beta releases before deploying them in a "production" server. I do that anyway with current SME7.x releases just to play safe, but it is probably a more important methodology to follow if using a beta release in production.
SME8beta6 is well advanced, some people would say it is not really beta quality software (meaning the code base is stable), it's just a case of it not yet being a final release due to lack of volunteer effort to get the product to final release stage.
I have used SME8betas in test for over 2 years now and never had problems, despite bug reports & fixes being regularly released. There is an issue with USB drive identification that is being worked on, which is considered a blocker to a final release.
If you need Centos5.x support, I think SME8beta6 is OK to use, just monitor updates carefully to avoid downtime.