Does anyone know which programs are "safe" and/or which ones are likely to get you a duplicate content penalty with search engines?

I know of CPShop, InstantCafe, and Flashpress.

Any others? Safe or dangerous?

It depends on how you use them. If you use them in a way as to duplicate the content of your shop then that risk exists. If you use them to provide a basis for a different presentation then there will be no penalty.

http://googlewebmastercentral.blogspot.com/2006/12/deft...plicate-content.html

Apparently there won't be a ranking penalty unless you're using "black hat" SEO techniques. Otherwise they pick one page to index and ignore the duplicates.

From the Google webmaster central link:

In the rare cases in which we perceive that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we'll also make appropriate adjustments in the indexing and ranking of the sites involved. However, we prefer to focus on filtering rather than ranking adjustments ... so in the vast majority of cases, the worst thing that'll befall webmasters is to see the "less desired" version of a page shown in our index.