##Code

// ==UserScript==
// @name        Stack Exchange: Underlined post links
// @description Underlines all links in questions, answers and comments on all Stack Exchange site.
// @version     1.0
// @include     http://stackoverflow.com/*
// @include     http://*.stackoverflow.com/*
// @include     http://serverfault.com/*
// @include     http://*.serverfault.com/*
// @include     http://superuser.com/*
// @include     http://*.superuser.com/*
// @include     http://stackexchange.com/*
// @include     http://*.stackexchange.com/*
// @include     http://stackapps.com/*
// @include     http://*.stackapps.com/*
// @include     http://askubuntu.com/*
// @include     http://*.askubuntu.com/*
// @include     http://answers.onstartups.com/*
// @include     http://*.answers.onstartups.com/*
// ==/UserScript==

var style = document.createElement("style");
style.appendChild(document.createTextNode(".post-text a,.comment-copy a,.wmdpreview a{text-decoration:underline;}"));
document.head.appendChild(style);

##About

Underlining post links has been requested and declined. This user script lets you chose.

###License

I hereby release this script in the public domain.

###Download

Click here to install this script.

###Platform

This user script should work in all major browsers. Plug-ins/add-ons may be required.