It does lead to weird moments when I realize that seemingly every Kaiser of the HRE in my game has a bride of my dynasty, and when family members go off to achieve great things without me forcing greatness upon them: my brother somehow became Pope
I have a game going where I started as House Cerdicing (petty kings of Wessex in 769). I now control an HRE that includes all of Brittania, Francia, Germania, Italia, most of Scandinavia, and Lithuania. The last eight Popes have all been Cerdicings, and that's without me even meddling in Church affairs. I like to think they just keep electing them to keep on my good side.
Bit weird though in that England remained Anglo-Saxon (and will remain so, now that the Norsemen have been pacified and all France lies under the Anglo-Saxon yoke, hence no Norman culture and thence no English culture). So many Oswealds and Wulfgars and Saexbalds...
EDIT: Anyone else noticing a problem with defensive pacts after the latest patch? They're still forming, but they don't intervene at all. I'm at 95% threat, and yet when I'm thinking of declaring war, it only shows the target's immediate allies as getting involved (and this holds up to the test). Wondering if it has to do with forming the HRE, and/or switching to an Imperial administration as well...