EDIT: Now out of beta. Fully implemented.
EDIT: You can now get the module from http://drupal.org/project/field_extract and it works properly with Drush.
My incredibly useful field_extract module is now available on drupal.org. I am slightly embarrassed because something went wrong in the project creation process so the actual URL is:
And when you download it the module comes inside another folder "1158878". In fact this will work just as it comes, you'll just get the folder 1158878 in your modules folder with field_extract inside that.
If you're competent you can extract the inner "field_extract" module and get rid of the outer 1158878 folder but, as I say, it should work out of the box anyway. (I may get around to re-uploading it properly at some point but I can't wait any longer to get it out to you.)
So what does it do? For a start, this is only a developer's module. It does nothing by itself and should only be downloaded if requested by another module. But what it does do is provide a couple of functions that make it much easier to extract field data from entities.
The project page provides clear instructions on how to use it.