Read somewhere that updating/upgrading from Wheezy Beta eventually to Wheezy Stable using the "wheezy" named repos (not "testing" named ones) has potential problems, and the best option is a clean install of Wheezy Stable. True or false? I've read the Wheezy Beta install docs, and the upgrading method is listed an "approved" option.
I do not know where you read it... From my personal experience, I did several upgrades (I love to tinker my systems, and when I was learning to use debian I was used to start from the stable version) from stable to testing when it was not even frozen, and sometimes upgrades from testing to unstable, and I never had any problem.
Just follow the recommendations you will find on debian's wiki/forum, which means using aptitude safe-upgrade (or something like that) and you could even be able to rollback the upgrade if something goes wrong.
Now that testing is frozen, I think this is even more unlikely you will have problems, but you could, if you have very specific configurations, I guess. But everything is always possible, I simply think that it is very unlikely you will encounter troubles.