I ran the 1.6.8a to 1.7.0 upgrade a few days ago. I got some errors during the mysql upgrade, but oddly enough the server started OK and reported 5.1.30, so honestly I didn't dig too far into it.
Today, the server is working properly, but I'm seeing this when I connect to one of the databases using the Navicat client:
ERROR 1577: Cannot proceed because system tables used by Event Scheduler were found damaged at server start
Not really sure what the Event Scheduler is...
I've been trying to run the mysql upgrade bit separately.
[root@thebuzz /opt/lampp/bin]# ./mysql_upgrade -u root -h localhost -p --verbose
Looking for 'mysql' as: ./mysql
Looking for 'mysqlcheck' as: ./mysqlcheck
...lots more OKs...
./mysqlcheck: Got error: 2013: Lost connection to MySQL server during query when executing 'CHECK TABLE ... FOR UPGRADE'
FATAL ERROR: Upgrade failed