You should probably at least make sure that each post is unique though, looking at the source that's why I kept getting the NOT STARBUCK one, it's been submitted multiple times
You can get around it by firstly removing any message that isn't unique, and it might also be a good idea to have a timeout where you don't accept another submission.
Clearing the input box between submissions would stop people from just clicking the share button multiple times too, then they'd at least have to paste the text in before clicking submit again.
Also consider this scenario:
javascript:for(var i=0;i<10;i++){$("#thought_message").val("spammy message");$( "#new_thought" ).submit();};void(0);I've filtered dups and cleaned up the submit process so it makes it a little harder to spam, but I guess it just seems silly to me to try and actually stop spam on the internet.