If you have been using plasmature upload types in custom modules, you should review that code. While most existing code should work just fine, it will not take advantage of the asynchronous upload capabilities.
To use the new types, you need to include the plasmature upload types within reason_package:
reason_include_once( 'classes/plasmature/upload.php' );
Basically, AssetUpload has been replaced with ReasonUpload and image_upload with ReasonImageUpload.
They should be compatible with the same parameters as the old types, but also have some new options.
When we get a chance we will try to post a tutorial on using the new ReasonUpload and ReasonImageUpload types.