@jaubourg its pretty hard or maybe even not possible to distinguish traversing methods perf, from others methods perf (DOM manipulations, event attach, etc.) in real-live code, you always use them together, because if you travers, you got a reason for it, but it does not mean they will not have final impact on your app, that makes it slow.
@dmethvin maybe you meant that traverse method is not bottleneck in most apps? They very common by themselves.
You already have extra code paths for IE, this is the exactly the same thing. Current code is not a slouch, but like i mentioned before, if you use traverse methods one after another, they might became slow -- http://jsperf.com/etapi-cumulative-effect