The issues with the anonymous download are:

- Increased support: people are going to lose the email/not get it, get disconnected half-way though downloading, try and pretend they got half way and try it again etc etc. This will require support staff, which if the site is large is not trivial. This leads to:
- Interface resend the email and perhaps track which emails have recived what

Which leads me to question your business process since you must track:

- Customer info to make the financial transaction
- Email address against which files they have purchased

so you have the same info as a registered customer (and more) so why aren't you forcing registration which gives you:

- Marketing statistics
- product performance by demographic
- increased security against fraud
- community networked
- customer satisfaction as they can come back and download if they lose file. Do they buy one download opportunity or the right to access to the information?
- etc

These would seem to be a good case _for_ the customer registration in the case of file download. Whats the case against?

- Extra click: then extend the module to auto download from the "thank you" page at the end of the transaction, but what if there is more than one file at a time?