Plus one buttons are easy to implement (see Google +1 your website). Pages render fine when using the code provided by Google. I wasn't the only one, however, who experienced problems, while validating my HTML5 pages. After updating them with +1 buttons and running them through the validator.w3.org site, complaints were returned. So, a validation error for the g:plusone tag can be expected . Then, I successfully replaced this XML element (for example, on the page www.axeleratio.com) with the following code:
Further information is available on the Google code site: code.google.com/apis/+1button.
Keywords: HTML5 conformance, markup validation, social networking, professional networking, friend grouping, online sharing, bookmarking
References and resources
 The Official Google Blog: Introducing the Google+ project: Real-life sharing, rethought for the web [googleblog.blogspot.com/2011/06/introducing-google-project-real-life.html].
 Google: Recommendations when you want them [www.google.com/+1/button].
 Digital inspiration: The Google Plus One Bookmarklet [www.labnol.org/internet/google-plus-one-bookmarklet/19474/].
 Pixelflips: Google +1 Button Validation Error [www.pixelflips.com/blog/google-1-button-validation-error/].
 Drupal: Google Plus One HTML5 tag [drupal.org/node/1180396].