I've just uploaded an updated version of the PsiViewer plugin, which should work better with recent versions of IntelliJ. Andrew Armstrong was kind enough to release the original source code to me, the code is at: https://github.com/cmf/psiviewer. Jon Akhtar and I will be maintaining the plugin, thanks to Jon for the vast majority of the fixes to this version.
The plugin now has an error reporter, please send us reports so that we can continue improving the plugin. We also have plans to fix up some problems with the original plugin and, longer term, to add support for visualising symbol resolution and formatting blocks.
Edit: there's also a public issue tracker at http://sylvanaar.myjetbrains.com/youtrack, feel free to file issues there.