Could you list available software programs or scripts that would allow
one to set up a membership-type web site for the "sale" of ecards
(electronic greeting cards that are sent and retrieved via the
Internet).  Any such software program or script ought to allow for
interfacing with credit cards, paypal and/or other over-the-internet
payment systems.  Any information on features, user base, user forums.
user reviews, ease of use for the non-programmer or other items that
would help in the selection of a program or script would be helpful.

The eCard feature is normally setup on a sight to attract traffic. I
don't believe there is a commercial one available that charges the
sender or reciever for eCards. It is normally a free feature on a
website. You would probably need to have a programmer create this for
you.

There are acctually plenty of programs/scripes available online. 
Try this site: http://www.ecardmax.com/
This program costs around $300 and provides most features that other
sites provide. The forums are not directly supported, but it does
support integration with other php forum scripts available. As for
non-programmer scripts, any script would be tough to implement, some
technical expertise will be required. But to make things easier they
do have a "Request Installation" section, that installs the script
directly to your server (Makes job a little easier)