Hi cpg and gboudreau,
I guess I got the issue mitigated. gboudreau suggested to run
mysql -u greyhole -pgreyhole greyhole < /usr/share/greyhole/schema-mysql.sql
After that the service immediately started and everything looks ok so far. Log is ok, files are in place.
I looked at the migration script and though I'm no expert in SQL I cannot spot the difference compared to what the terminal command does.
For completeness, here's my /var/log/monit: http://pastebin.com/6vzW11sx
Doesn't show much. There is one older copy but that looks the same (same messages, just different time stamps).
So the best conclusion that I can draw is that (i) most probably I experienced the issue that cpg suspected from the beginning and (ii) most probably something's not correct with the ruby script. Maybe you can draw more/other conclusions?
Could it be related to the fact that I installed the beta some 14 days ago, presumably I started with an earlier version then? Might explain why others do not experience this. Just speculating.