Open your People app, hit the little People icon with the circling arrows on it. This is everyone's birthdays and upcoming events.
Very useful for birthdays. On this screen, you can hit Menu > Settings, and turn on Event notifications, so that it actually gives you a Notifications for peoples' Birthdays, etc.
The direct links to peoples' profiles, within their contact list, as well as the picture and birthday notification, photo upload, and status update, make Facebook for HTC sense just fine for me.
I think it's designed to not force LOTS of facebook features onto you (like the Facebook App) and notify you for every little thing, but build in a LITTLE bit of Facebook, so that you can use Facebook Mobile or Touch or the App if you want more.
I think people who aren't 'heavy' facebookers appreciate the subtle inclusion of Facebook into HTC Sense. I think if they synced their phone and were getting all kinds of messages, notifications, events, and so on popping up by default (or even by accidentally turning on the notifications at some point), many novice Android users who are NOT heavy facebookers would be a little bit overwhelmed.
I like the subtleness of it.