I know I personally cannot tell the difference between the example comparisons in the post. Not sure my users would. I'll probably a/b test it with them at some point to be sure. Until then, my impression is that vectors are a net positive.
The difference is irritating and clearly noticeable for e.g. the "Documents" icon if you compare it to the "Go" menu. And it's not because the big versions are bitmaps, it was mostly the missing outline and lack of contrast.
(I still find them much faster than the monochrome versions (and with a smile) :))
The Finder's "Go" menu is really a good example of tiny, clear icons.
Oddly the .ico format allows different versions for different resolutions, unlike most ther formats.