The Messages window menu item is disabled, so the only way I can see the compilation errors are with tooltips, which is annoying (and which also makes it hard to copy/paste errors to report problems).
Is this a known issue in the current plug-in?
Please file it here: http://youtrack.jetbrains.com/issues/KT
For future reference: http://youtrack.jetbrains.com/issue/KT-1622 (run a build to make the messages window appear).