It really matters. Of course new domains are much more professional, however, if you don't need SEO, and it's only for your list, then sub domains are fine. Personally, I only launch great products that I know will benefit others, so I don't look back at all when buying a new domain.

^ Truth right there.

If you make a quality product, people are going to purchase it. Whether or not its a stand alone domain or a subdomain, as long as the sub-domain is connected to some sort of generic standalone domain.

Thanks for the info.

I have a weight loss blog. There is where my subscribers are coming from. I am planning of selling quality weight loss ebooks and considering putting each ebook's sale page as subdomains on my blog site.

The marketing of the ebooks at this time will be telling the subscribers about them in the newsletters. Most of the newsletters will not be selling products. They will be weight loss information content.