If you offer any downloads on your site and you are not getting anything in return for them - why not build your twitter following by installing the free Tweet & Get it plugin. What it does is forces people to tweet about you before they get the download. Obviously this restricts who can download your file to people who have a twitter account so its not ideal if you are trying to maximise your downloads, but if your target audience are likely to have twitter accounts then it can be an effective tool.
Install The Plugin
Download the plugin and unzip the file, then in your WordPress admin, visit “Plugins” > “Add New” > “Upload” and upload the file.
Activate the plugin and you will see a new menu item called "Tweet & Get it".
Create Your Button
On the new menu, click the "Make Your Button" link and you can begin setting up your first button. You will need to enter your twitter username, a message that people will tweet out ( make sure to include a link to the download page and your twitter account ), then you can upload your file or link to an existing one online :
Hit "Create Your Button" and you can then place it within your site.
Place Your Button
Once you have created your button, the plugin creates a special shortcode for you :
Save your post and view it and you will see the button which looks like this :
When a user clicks the link, a popup appears where they have to login to twitter if they aren't allready, then this confirmation appears, when they click ok, the tweet is sent and they can then download the file.
I have just installed this plugin for my free WordPress themes so I cant comment on the effectiveness yet - I will update this post after a week or so of testing. I think sending a tweet is a small price to pay if you are offering something good for free download. I have seen this plugin work really well for other people. My only concern is people without a twitter account not being able to access the file, if they really want the file - twitter is quick and free to signup for so I suppose they could do that. I wouldnt recommend this plugin if your aim is to maximise your file downloads.