I've participated in only 3 different families' Passover Seders, so my experience is limited in terms of different families' traditions. How widespread is the custom of eating a hardboiled egg in ...
What is the appropriate way to prepare the Beitzah for the Seder Plate?
The Halacha is not to eat roasted meat at the Seder, therfore you can not eat the Zeroa at the Seder. Can you eat the roasted egg (Beitza) at the Seder? (sources)