Google doesn't like doorway pages, but mini-sites, if done correctly will have no problems.
We use more than 200 domains for our hosting company. Each one of them are showcasing our website in a different light.
Google doesn't like duplicate content or misleading sites - however you can easily use multiple sites and then point them into your main site (or checkout area).
For us, our sites are stand alone sites with 5-10 pages of information and then a link to our order page.
Creating junk sites, mis-information sites, or sites that just spew RSS feeds are not what we're talking about in this case. We're talking about true individual sites that then link to other pages or order forms.
I also wanted to clarify that these are not redirect sites, doorway pages/sites or things of that nature. These are targeted niche sites that are dispaying content and links to our order forms - no adsense or banner networks. No other form of revenue generation. For example, we use and sell a product called X-Cart (and online shopping cart software). We have a specific site setup with all the details for X-Cart and how it works in our system. We also have a specific site for X-Cart Cloud applications, and ones for various other shopping cart and online forum software.
These are individually designed sites with their own themes, templates, content and other information. No violation of Google Guidelines when you do it this way. The violations happen with doorway pages.