What prevents a person from buying the disc and then doing returns for a hundred others, all for the price of one disc?   also, does any personal info reside on the disc after it has been ejected from one's computer?  Thanks

Nothing other than the software license precludes one from using the software as a paid tax preparer.   Also, the software has to be installed on your computer, nothing is stored on the TurboTax servers.  You prepare the returns and they are saved to your computer.  You have to register the software, where you will agree to not use it professionally.  No one will be keeping track of how many tax returns you have prepared.  Here is the software - EULA 

And no, nothing stays on the disc - but the disc can only be registered to one computer..;)

forgive my ignorance and thank you for your indulgence:  so in order to get multiple filings off of the disc, they would all have to be done on my computer, correct?  

Yes, pretty much.       Although, you can load it and use it on more than one computer in your household.  But you can only e-file from the 1 registered installation.  You can transfer tax files between computers if you need to.  Does that make sense?  

So after I register the disc on my computer, I could loan the disc to a friend who is outside of my household and my friend could do their return and print it out and mail it in? Along with all the hard copy attachments?

I don't think it will work because the registered license is only for your computers.

According to the software licensing agreement, the CD can only be installed on computers that YOU own.

Thanks very much to both of you.  Great info provided and quick too !