If I forget, or deem the journal entry to long after posting, I know that I can click on 'add a comment' or anything else that gets me to the entry itself and then click on the blue pencil icon near the top to edit the entry. I do mourn the lack of an edit feature for replies, tho.
This post brought to you by the knowledge that several people on my friends list are new and may not know it. There's a wealth of knowledge in that FAQ if you can get past the dead-dull basic stuff at the beginning.