I have tried the upgrade - I just installed Magento on Sunday (one day too early).
Using the Connect Manager I see the Packages and when I press ‘Check for Upgrades’ sure enough Version 1.3.0 appears. (the summary says release for 1.2 though!)
However in the ‘Actions’ drop down I just see ‘reinstall or uninstall’
I then entered the key David had and a window opened which said
“Ignoring installed package magento-core/Mage_All_Latest
Nothing to install”
I then went out into admin - returned into Connect Manager - pressed ‘Check for Upgrades’ and the Version 1.3.0 appears again.
Just that this time ‘Upgrade’ was there.
It worked perfectly then.
I have to say with just 72 hours of using this program it is just like old times - I have had innodb issues, permission issues coming out of my ears but I have to say when it works it has an air of quality about it. I have got so use to Joomla/VM installs that are rock solid that this return to the hours of frustration and then a sense of joy when a breakthrough is made is quite nice:)