Currently, the arrowheads in tikz are always straight, as if terminating a straight line. This is not a big deal in most cases, however, when working with small scales the arrowheads look outright displaced and require manual tuning. Tikz Circuit library is quite heavily hit by this misbehavior, because the internals of the symbols and annotations are drawn in the [-1:1, -1:1] coordinate scale, so it is almost impossible to get right looking arrows terminating circular paths (a readily available example is "circular annotation", but quite a few other special purpose symbols require similar marking).
On the other hand, Metapost seems to handle such cases just fine, because of some sort of arrowhead bending algorithm implemented there (section 9.6 of the metapost manual has a brief description). Is it possible to have something similar in PGF/Tikz?