For example the Tidypics plugin has two methods for the image entities: addView() and getViewInfo().

When a user views an image the first one creates an annotation named tp_view for the image. The user who viewed the image is set as the owner of the annotation.

The latter function counts the amount of the tp_view annotations for that particular image.

You can take a closer look of these methods in the file tidypics/classes/TidyPicsImage.php

You could create a plugin that has similar functions. This plugin could add a new item to the blog's entity menu to display the total count of views.

To save the annotations you could for example override the view blog/views/default/object/blog.php and create a new annotation every time when displaying the full_view.

So there's some quick examples that came to my mind...

That's exactly what views counter does - and it does it for blogs: http://community.elgg.org/plugins/872625/1.1/views-counter-18x

@matt Nice plugin! How does it keep count of the views?

it just counts the 'views_counter' annotations associated with each object

@matt I mean how does it know when to create one of those annotations? How does it know that user is viewing an entity?

@juho : extend the entity full view.

ah, yes Juho it's a view extension on full view (though I remember there being a bit of wierd logic there for some reason... it's documented inline I'm pretty sure) that annotates the $vars['entity']

I had some problems with view counter before... but Ill give it a go again