It's not missing for me. Did you accidentally log yourself out?
No. This is bizarre. It was working earlier when I posted my Christmas contest on the other side of the board and I made several edits to that thread. Now the EDIT button has vanished from my posts and I am logged in. Now I can't make changes.
Has anybody who is having this problem, tried hovering their mouse over there it is, to see if there is a still a clickable link there and you can still edit? It's to the left of the Report Abuse button.