Forgive me if I ramble somewhat; but I think all this information is important.
I'm really super excited to see what Joomla 3 will do for me on some of the sites I manage. First and foremost is my company's own site. That site is Joomla 2.5.8 and uses K2. This is primarily because I bought a template from a third party that uses K2 and some other plugins. (I wasn't particularly excited to add all the complexity to my own site but I wanted to get it online so I gulped and went forward.)
So, after a backup I decided my best approach was to unzip (via the command line) the file "Joomla_3.0.2-Stable-Update_Package.zip" over the top of my installation. I presume that this is the proper approach, as I was unable to find any documentation anywhere explaining the best upgrade method.
This naturally immediately completely broke my site.
After restoring the site from backup, I knew that this was not a turnkey operation. So I created a test fork of my site and tried again. This time I found that I had to (and did) update K2 and RokMenu to the latest versions. I also noted the mootools fixes for the framework and made those. After doing all of that, the site sorta works. The homepage looks perfect but the interior pages are completely broken. Also, the administrator pages seem to mostly work but look very funky. (I'm including a snapshot.)
The item that concerns me the most is the interior pages of my site that are broken. I've looked at the server logs and I find that each page load aborts with this kind of error:
[Wed Dec 26 17:27:13 2012] [error] [client xxx.xxx.xxx.xxx] PHP Fatal error: Call to undefined method JParameter::loadINI() in /var/www/vhosts/testing.mysite.com/httpdocs/libraries/joomla/html/parameter.php on line 76, referer: http://testing.mysite.com/index.php/
My thoughts are that perhaps Joomla is discovering old code that might be removed by a better installation method(?) I'm only guessing here, as I'm over my head with the organization of the software. Any ideas where to go from here?