Hi Paul,
The drag/drop gesture from a requirement to another requirement is used to create a parent/child relationship (i.e. nested requirements), so you will need to create references via the Requirement Details form. I guess we could add a variant drag/drop gesture to create references, e.g. Shift+drag or right-mouse drag. Definitely a power-user type feature since it wouldn't be very discoverable. Is the select referenced requirements dialog sufficient, or does it become unwieldy after a certain number of requirements? (Keep in mind that you can sort requirements by multiple columns by shift-clickin on the column headers in the selection dialog). Other thoughts?