Well, I guess that headline will get some attention.
But seriously, DO NOT attempt to update to 6.0 unless you are working on a cloned test server because you will almost certainly have issues. In fact I wouldn't even attempt an upgrade until V6 has been around for a while and gone through at least one upgrade itself, to iron out the major upgrade headaches. The system is just too complex to expect it to go smoothly at the outset.
I've always been able to upgrade easily and seamlessly within 5.X but this time even though I followed the new instructions perfectly it failed with unrecoverable errors, and I was not able to restore the old version and DB for unknown reasons (I had never attempted a DB restore before) - I got a really weird error.
See my previous post which so far has no replies - not surprising - it's a cryptic error problem which few can really decipher, and that's the whole problem here.
We are using Drupal because it supposedly obviates the need to know a lot about code and system administration crap. But the update process needs to be much more automated. It's really an extraordinary pain in the neck and fraught with difficulties - not for the faint of heart. Great strides have been made to simplify site admin and theming, for example, but this is the next big hurdle.
Just for example: