Regarding performance: it will get much better once browser have implemented http://www.w3.org/TR/2014/WD-shadow-dom-20140617/. Shadow DOM is not easy to polyfill (especially because of some issues in how the browser's C++ objects were presented to JavaScript as prototypes.)
Regarding IE failures -- do you have any more information? All of the elements should be cross platform. It would be great to file these issues at https://github.com/Polymer, if you haven't already.
Regarding IE failures -- do you have any more information? All of the elements should be cross platform. It would be great to file these issues at https://github.com/Polymer, if you haven't already.