Providing buttons to vote for blog posts in social bookmarking services has become quite popular with many bloggers. In theory, they are a good way to gain exposure and attract more visitors. In reality, these buttons often just turn out to be more or less advertising for the social service itself rather than for one's blog and may even be seen as attention whoring by visitors, when overdone. So this is a feature to use with care.
Traffic from the social media is not actually very social at all. The typical social media user is primarily interested in whats new on the web and being offered dozens of links per day, will only dedicate a very short amount of time to briefly scan each of them. Social media users are generally ad blind, rarely read more than the one article, they came for and usually don't subscribe or comment. They may convert into blog readers, but in the majority of cases, this requires featuring regularly in the social media service of their choice and accepting a large volume of "blind traffic" in return.
In order to benefit from social services, it is not sufficient to just add voting buttons/links to blog posts and hope for the best. Even articles that are "meme worthy" will only just produce a short traffic burst on their own.
The unfortunate truth about social media services is that every website owner wants a share of their traffic and only those who can "seed" voting have a chance of succeeding. In other words, in order to get traffic this way, a considerable subscriber base is usually needed first, that is willing to upvote blog posts to a level where it gets the attention of the rest of the social media user community.
With Drupal, adding voting buttons can conveniently be done by using either the service_links or the addtoany module. However, keep in mind, that a whole array of these under each post will make the blog look cheap on one hand, while not being that useful on the other.
In order to cast a vote, all social bookmark services require the voting users to be registered and logged in. Also, power users will likely have a browser toolbar installed with a voting widget of it's own. In essence, this means, that only a tiny fraction of the visitors of one page will actually find voting/submit buttons useful, so they will only make a difference on high traffic blogs.
The best position for the service links block is arguable below the main content area and preferably even below the page fold. The reason behind this is to make downvoting harder. People, who disagree with an article are less likely to read it entirely, so putting the downvote link out of direct sight makes it less lightly to be spotted and pressed. On the other hand, people who do agree with an article are likely to read it entirely and will then automatically see the upvote button when finishing it.