It's not bad but the fonts in a default wireshark installation don't look too great. They look jagged and the font used is too thin and too large, particularly in the menus.
Finding information on customization has been pretty difficult but this is what I have come up with as a workaround. To change the UI font that wireshark uses, edit the pre-gtkrc and gtkrc files included in the Wireshark installation. Open up these files in your favorite text editor, which are located inside /Applications/Wireshark.app/Contents/Resources/themes/Clearlooks-Quicksilver-OSX/gtk-2.0. Search for the entry in each configuration file named "gtk-font-name" and set it to whatever font you want. OpenType fonts don't seem to display as well as TrueType fonts do, so for this example, I've changed this value to "Candara 11" from the theme default, which was set to "Lucida Grande 12". Restart wireshark and if you used the same fonts as I did, you get something like the following:
This is a little bit better but the text still does not look as if font-smoothing is set. This can be fixed as well though by making a change to the fonts.conf file located in /Applications/Wireshark.app/Contents/Resources/etc/fonts and adding the following text:
<match target="font"> <edit mode="assign" name="autohint"> <bool>true</bool> </edit> </match>
Restart wireshark (I also restart xquartz after each change but you really shouldn't need to do that) and you get something that looks even better:
Keep in mind that this is just a workaround. Updated installations of wireshark will most definitely over-write these changes.