I am sure someone will roll a module very soon, but in the meantime I thought I would blog about our first experiences in adding the plus one button ...
There is plenty of background on the google plusone button already - http://www.google.com/+1/button
It sounds very simple, and indeed it is - with only one small gotcha that we couldn't find any documentation for. We basically followed the steps outlined here : http://code.google.com/apis/+1button/ which is simply :
Work out the layout of your plusone button, there are a couple of options - all with varying degrees of "in your face"ness. You can do this here http://www.google.com/webmasters/+1/button/
Add a special tag in the location where you would like your plusone button to appear - there are HTML4 and HTML5 versions of this available, if in doubt go with the HTML4 one. Your tag will look something like this
And that's it ... well at least that should be it - however we just couldn't get this configuration to work, we consistently got a red exclamation mark after clicking the plusone button. After a bit of experimenting we figured out that the URL of the current page needs to be "forced" into the plusone tag in an href attribute - giving something like
<g:plusone href="http://www.computerminds.co.uk/about" count="false"></g:plusone>
Obviously you aren't going to hardcode this URL - but instead populate the href attribute using a smidge of PHP - something like
<g:plusone href="<?php print url($_GET['q'],array('absolute'=>true));?>" count="false"></g:plusone>
And that should do it ... don't forget you need a google profile https://profiles.google.com to use plus one ...