Good article found at Matt Cutts Blog

When youre starting out at SEO, think carefully when youre deciding whether to buy a software package (or service) that promises SEO results. Why? First, when youre making pages yourself, theres a limited amount of pages that you can make a mistake on; when youre using software, any damage can be amplified a thousand-fold. Second, you should really know what exactly the software is doing. If you buy a piece of software that makes many doorway pages that do sneaky JavaScript redirects, that can raise a red flag to search engines. I bought this thing and didnt know what it would do is not a great explanation for a reinclusion request, because youre ultimately responsible for the pages that you make on your domain. A third reason is that if you decide to buy a particular piece of SEO software, other people might be trying it too, and lots of people all using the same software package can lead to your site attracting more scrutiny.

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