It mostly works but you can still run into issues when you e.g. want to have an element size match the border of another. Things like that that used to work don't anymore due to the tricks needed to make fractional scaling work well enough for other uses.
The problem is the rounding from fractional sizes due to fractional scaling to whole pixel sizes needed to keep things looking crisp. Browsers try really hard to make sure that during this process all borders of an element remain the same size, but this also means that they end up introducing inconsistencies with other measurements.
