There was a recent change made to the Counter Clockwise plugin for Eclipse where it is now required to press "Ctrl + Enter" to send a command to the REPL Server in the command window. In the past you just needed to press the "Enter" key.
This drove my crazy for a few days and just wanted to share.
I posted this reply in the REPL and Eclipse thread where Ned commented on this but I'll repeat it here as well:
Just so folks know why: the CCW REPL has full structural editing, just like in the main editor - so enter inserts a newline and indents code. Unless you are at the end of a complete top-level form. You used to have to press shift-cmd-x (I think? at least on Mac OS X) to submit code when you were in the middle of a form - the shortcut for execute current form under the cursor when you're in the main editor. ctl-enter is a nicer shortcut key for submitting code and it's more consistent to make enter always behave like the editor and ctl-enter always submit the entire form. This may seem odd if you're not used to the strict structural editing mode - which I set as the default, as do most Clojurians - since this matches paredit in Emacs. Once you get used to paredit / strict structural mode, you'll never go back!