huhu martina: den code gibts in den google webmastertools!
oder unter:
http://www.google.com/webmasters/+1button
tipp: unter erweiterten einstellungen u.u. den link zur startseite hinterlegen, damit nur diese “geplused” wird 
oh und zu deiner frage, was es bringt:
The +1 button and search results
How does +1 affect search results?
+1 helps people discover relevant content—a website, a Google search result, or an ad—from the people they already know and trust. Adding the +1 button to your pages lets users recommend your content, knowing that their friends and contacts will see their recommendation when it’s most relevant—in the context of Google search results.
When a signed-in Google user is searching, your Google search result snippet may be annotated with the names of the user’s connections who’ve +1’d your page. If none of a user’s connections has +1’d your page, your snippet may display the aggregate number of +1’s your page has received.
Does +1 affect my site’s performance in search?
Content recommended by friends and acquaintances is often more relevant than content from strangers. For example, a movie review from an expert is useful, but a movie review from a friend who shares your tastes can be even better. Because of this, +1’s from friends and contacts can be a useful signal to Google when determining the relevance of your page to a user’s query. This is just one of many signals Google may use to determine a page’s relevance and ranking, and we’re constantly tweaking and improving our algorithm to improve overall search quality. For +1’s, as with any new ranking signal, we’ll be starting carefully and learning how those signals affect search quality.
How will the +1 button affect my traffic?
Personalized annotations next to your page in search results may increase your site’s visibility and make your site’s snippet more compelling, which may in turn increase the odds that users will click through to your page.
Will +1’s from my site show up in search results?
If a user +1’s a URL on your site, the Google search result snippet for that URL may be annotated in search results and search ads.
However, your site may make the same content available via different URLs. For example, your site may have several pages listing the same set of products. One page might display products sorted in alphabetical order, while other pages display the same products listed by price or by rating. For example:
http://www.example.com/product.php?item=swedish-fish&sort=alpha
http://www.example.com/product.php?item=swedish-fish&sort=price
If Google knows that these pages have the same content, we may index only one version for our search results. As a result, +1’s for the other versions may not appear in search results.
You can make sure Google displays +1 annotations for the most search results possible by adding the rel=“canonical” property to the non-preferred versions of each page. This property should point to the canonical version, like this:
<link rel=“canonical” href=“http://www.example.com/product.php?item=swedish-fish&sort=alpha”>
This tells Google: “Of all these pages with identical content, this page is the most useful. Please prioritize it in search results.”
Now, when a user +1’s a page with a non-canonical URL, Google will associate that +1 with the canonical, preferred version. More information about canonicalization.
How does the +1 button affect my ads?
The +1 button itself will appear next to your headline on search ads. Personalized annotations will appear beneath your Display URL. For example, Maria +1’s a page selling a neat laptop holder on a website. When a search ad with that same URL appears, her friend Sam might see the ad with the note “Maria and 28 other people +1’d this.”