It really annoys me how large the font and icon sizes are for Wireshark in MacOSX. I found someone else who had posted how to adjust the sizes, and for my own reference as well as anyone else who happens to find this page here is the diff:
diff ~/Wireshark-correctfontsize-pre_gtkrc /Applications/Wireshark.app/Contents/Resources/themes/Clearlooks-Quicksilver-OSX/gtk-2.0/pre_gtkrc526c526
< gtk-font-name="Lucida Grande 9"
---
> gtk-font-name="Lucida Grande 12"
528c528
< gtk-icon-sizes = "gtk-menu=16,16:gtk-dialog=24,24:gtk-dnd=32,32:gtk-button=20,20:gtk-large-toolbar=16,16:gtk-small-toolbar=10,10:inkscape-decoration=6,6"
---
> gtk-icon-sizes = "gtk-menu=16,16:gtk-dialog=48,48:gtk-dnd=32,32:gtk-button=20,20:gtk-large-toolbar=24,24:gtk-small-toolbar=16,16:inkscape-decoration=12,12"
I also hacked a quick script to just edit the file since it gets replaced every time you download a new version. You can find the script at: http://tp.org/jay/download/Wireshark_font_fix
Also, if you're having problem with the font characters all coming up as Rectangles on MacOSX 10.6.3 and certain development versions of Wireshark (1.3.5) for example, you may want to check out Wireshark Bug 4697. You can change line 73 of the /Applications/Wireshark.app/Contents/Resources/bin/wireshark script to:
sed 's|${HOME}|'"$HOME|g" "$TOP/etc/pango/pangorc" > "${HOME}/.wireshark-etc/pangorc"