Magento CE 1.9 has been released. It appears to be a relatively small update introducing a new responsive GUI. See the release notes here.
Here are my notes after upgrading my dev store from 1.8.x to 1.9 using the command line.
Backup existing install folder and database
1. Magento source
tar -cvvf /home/backup/magento.tar /home/www/magentoinstallfolder/
2. Magento DB
/usr/bin/mysqldump -h localhost -u USER -pPASS magento | gzip > ~/backup/folder/db-magento.sql.gz
1. Remove cached files and temp files
rm -rf downloader/pearlib/cache/*
rm -rf downloader/pearlib/download/*
rm -rf downloader/var/cache/*
rm -rf downloader/var/report/*
rm -rf downloader/var/tmp/*
rm -rf media/catalog/product/cache/*
rm -rf media/tmp/*
rm -rf var/cache/*
rm -rf var/session/*
2. Restart memcached (if being used)
3. Sync mage
4, Run upgrade
5. Reset ownership and permissions on all files and folders.
Check Magento is operational, login and refresh caches.
If all is well take a well deserved break and maybe eat a cream cake. If all is not well restore from backup…