Problem: When posting via the web client, LJ users are told that the process timed out, so they post again. This results in multiple copies of the same entry.
Solution: This is a browser error, not a LiveJournal error. Copy the text you've just written and paste it into a text editor on your computer. Then go to the page you were trying to post to (your journal, a community journal, a comment to someone else's journal, etc.) and see if your post has arrived. If not, *then* you can try posting it again, but usually it shows up on the first try.