I didn't have any. Problems that is.

I upgraded six sites yesterday and today, didn't have a single issue with any of them, and I have quite a few add-on modules as well.

Not to knock Drupal, but after several years with that CMS, my main issue was that after almost every upgrade I did, something broke on my site.

Anyway, wanted to say thanks to the C5 team, keep up the good work, you'll keep people like me!

(and this was from 5.3.3.1, I haven't used the new cool update for 5.4.x yet)