I have had the +1 button up here on WPLift since it was released - Im not sure if I have had any direct traffic increase because of it yet but I'm sure it will become more important in future as Google moves more towards social recommendations in their search results. With that in mind I'm going to take a look at the available plugins to add the +1 button and your Google Plus profile to your site.
Google +1 Button Plugins
WordPress Google +1 Button
Adds the Google +1 button to your website's posts, pages, attachments, and custom post types. Has a variety of options for button style and position, and exposes a wp_plus_one_button action for custom integration with the theme or other plugin.
WordPress Google +1 Button »
Google +1 Button Advanced
Plugin to add manually or automatically Google +1 button to wordpress contents. Choose where to add: top, bottom, both, manually in theme or in post/pagecontent.
Google +1 Button
Google +1 WordPress plugin adds a configurable Google +1 Button to your WordPress blog. You can set the title, alignment, size, background (and language) of the +1 button. Simply install the plugin and place the widget.
Google +1 Button
New Google+1 button allows your blog to be rated. The button also provides a current count of how many times your story has been liked on Google Search Engine.
Google +1 Button »
Google +1 Button Plugin
The WordPress Google +1 Button Plugin: Add +1 to your pages to help your site stand out +1 buttons let people who love your content recommend it on Google search.
Google Plus Profile Plugins
A simple plugin that adds a google+ widget for linking to your google+ profile and showing your number of followers
Scriptrr Google + Profile widget
Google Plus Profile Widget allows users to add plugin on their blog or website to invite visitors to new Google + Profile.
Google+ Plus WordPress Widget
Display the latest post from your Google+ Plus accounts inside WordPress widgets. Customize the number of post displayed and user allowed to include updates from Google Buzz too.