Windows is strict when it comes to file locking and so doesn't let leiningen delete its own plugin jar files. Print an error message when uninstallation fails.
RuntimeMXBean.getInputArguments is buggy when an input argument contains spaces. For an input argument of "-Dmyprop=hello world" it returns two arguments, split at the space: "-Dmyprop=hello" and "world". This causes eval-in-project to fail in spectacular ways when leiningen.original.pwd contains spaces or when path to the clojure jar that gets passed to -Xbootclasspath contains spaces (which it does by default on Windows XP).