One funny thing happened yesterday evening. Typically when I switch distros, I keep my desktop and laptop machines in sync and switch them both. That has proven to be valuable. As I was configuring my laptop last night... I was changing ownership of the /var/www directory and I messed up big time and changed the permissions recursively of everything in /var. Holy cow!
Of course that's a big deal because many of the critical running processes keep track of their status using /var and they sort of need the right permissions to access their control stuff. Took me a few hours to straighten that out. And having two identical installations allowed me to compare the broken one with the non-broken one and correct the ownership.