Google Plus's [+1] button is finding its way onto web pages quicker now and with good reason. The button has two cool functions when logged into Google. The first click is simply a vote endorsing the page. Then the button expands and allows you to say something about that page and share the link with an individual, a Circle of friends, or the Public on G+.
On January 10, 2012, Google moved the SEO goal posts yet again with the introduction of "Search, plus your world"... ie Social Search.Google now lets searchers see page results endorsed by people in their G+ network, which puts serious value on the [+1] button and G+ in general. Google is essentially adding human intelligence to their search engine as it builds its own social graph.
So what is the impact on SEO? Google hasn't directly declared what the effect is yet, however marketers are seeing that pages that receive many +1s are performing better (more from Ian Lurie at Conversion Marketing for more). In general, there does seem to be a correlation between links shared on social networks and their resulting search rank according to SEOmoz. The nuance here is that the improved rank is related to Click-Through-Rate... simply that the page is getting more traffic, which effects pagerank. Not a direct link to the actual action of a user hitting the [+1] button.
How do marketers impact it? Do we just need to hire a room full of button pushers to hit our [+1] buttons? No, that won't affect anything because its not about the number, its about the [+1] vote of people in a user's network primarily. I say "primarily" because when I look at my social search results, I'll just see +1 G+ comments from people in my G+ network. Secondarily however, I'll also be able to see the total number of people world-wide who have given a page a +1, which might also influence my decision whether to click or not.
Still it seems that good SEO comes back to creating engaging content and then using every means possible to share that content. Google's [+1] button is a new tool for getting that content out... if the content is worth the +1 endorsement.