I feel a bit weird because this is a really simple issue that apparently nobody has brought up so far but I find that very simple fractions produce output that looks vertically unbalanced. The following example uses Iwona as math font because there it's really obvious – with the gap between numerator and fraction line being almost 1.5 times as large as the space between denominator and the line.
\documentclass{standalone}
\usepackage[math]{iwona} % Iwona as math font
\begin{document}
$\frac{1}{2}\frac{1}{N}$
\end{document}
It's not completely a font issue though. I measured Computer Modern and the imbalance factor there is about 1.3, too.
I find this visually unpleasant and somewhat surprising – given how much LaTeX is hailed for its math typesetting, there is probably a reason for this imbalance. Either way, is there an easy way to fix this feature?