SearchEngineJournal.com just published a post entitled “17 Ways to Get De-indexed by Google”
Here are some of the 17 ways, but you should check out the post which details each of the 17 in-depth:
Cloaking
Duplicate Content
Writing Content with a Machine
Add Unrelated Keywords to Your Content
Joining Link Exchanges and Bad Neighborhoods
Point 100 URLs to One URL
Sending Automated Queries to Google
Scraping Content
Sneaky Redirects
Building Water-thin Affiliate Sites
Duplicate Sites…
