First:

Mifuyne wrote:

A person have downloaded all the .iso images of the Express edition softwares, in case they need to reformat their hard drive(s) and reinstall Windows. Then one day, their computer crashed or they decided they want to reformat. This had occured on November 10th, 2006.

It should first be made known that if you download the .ISO files and create CDs, you are, in a manner of speaking, "exempt from registration."  So if you went the route of the CD it shouldn't make a difference, except for the initial registration - however, you won't get a registration code - at least I didn't.

Second:

If they have to reregister after a reformat (or reinstall), and the reformat/reinstall was done after the promotional period's deadline, will they have to pay for the software?

I have had this happen already (reinstallation after a clean format and on the same machine).  While it did ask me to activate it again, I found that the email I got did not include a new activation code.  Also, once you have activated you should have open access to the benefits portal.

From everything I have read and or seen, once you activate you are set (since it uses a .NET Passport your information is recorded somewhere... I'm sure of that).  I know also that the CDs that you can create will ask you (or remind you as the case may be) to activate/register, but once you already have once, you don't have to again...  There is no 30 day limitation on the Express editions installed by .ISO (CD).