Have been using https://github.com/acreeger/meteor-moment in meteor and it works well, however is there a way to make the output of moment reactive so that it counts up "3 seconds ago", "4 seconds ago", etc?

You can now use the package copleykj:livestamp. (github | atmosphere)

Install it like this:

meteor add copleykj:livestamp

It has a dependency on momentjs:moment so it will bring that along automatically. It installs a universal helper that is available anywhere and can be passed a date object.

You can use it in a template like this:

<li>Regular:   {{date}}          </li>
<li>Livestamp: {{livestamp date}}</li>

Here's a working demo in MeteorPad