I've just started using Apture. It's a way of adding extra material for your readers without their having to leave the page, making your post richer and more interesting. You'll probably have seen this device on a lot of the online newspapers, where a word or phrase will have a small window that opens with more information, photos or video.
I did use Snap for a short while, but this is different. Snap just gave you a snapshot of a particular link and to be honest I found it annoying and it slowed down the page. Apture is not contextual advertising either, you choose which word or phrase you want to expand on and then you choose exactly what you want to show. You can choose a video, photo, text, link to a specific URL or post within your site and even embed a code. In fact, there are supposedly 50+ sources of multimedia.
To give you an example of a text link, this is some text about blogging from Wikipedia. Add an R to Apture and this is the song you get by Blondie.
What Apture does is make your posts much more interesting for visitors and keeps them on your site for longer. I, personally, wouldn't overload it, but that's a choice for each of us to make.
If you're an Amazon affiliate, you can also make some money in this way. This is an example of a link to a book - Problogger - which, by the way, I have constantly found to be a great source of information.
To start using Apture, you need to download - free - the add-on for your particular blogging platform. You can do that here. Once you've downloaded it, you go to your blog and a small dashboard will open up asking you to sign on. Then you just add the sites you want to use it on - for each site you will be given a code to install on the blog. One thing I would like to mention, you will be given the option to Auto-enhance when you add your blog, I would recommend unclicking this option, in order to have complete control over what links you want.
Take a look at this video tutorial produced by Apture. There are many ways of using Apture that I haven't mentioned, and this will give you a better idea.