What i have personally seen from client sites autoblogs tend to have a few things in common that get deindexed in google:
1. possibly linking outbound to attack sites(this occurs when you post an ezinearticle or something like it that has a link to an attack site with malware or some other low quality content). This looks very bad to google.
2.A domain and page authority ranking on seomoz of under 5-10 on average, i have seen a few that don’t fit this but if they are above they usually match another of the criteria set forth here.
3.They match whois, IP, adsense or link to another site owned and operated that has been deindexed. A lot of the time sites get mass de indexed simply by being guilty through association. Google has ways to determine if your a bad neighbor.
4. Many of the sites seemed to have numerous issues ranging from robots.txt issues to high numbers of 302 errors. Many of the coolhandle sites i looked at had permissions issues set at the hosting level as well. Not conclusive but it popped up a lot.
5. A lot of the first deindexed domains seemed to be getting decent traffic then dropped off, day later numerous other sites on same ip hit. This might point to traffic levels that could incur a human review at which point a mass deindex occurs.
6.Very little to no backlinking – common theme among almost all of the deindexed sites was either no links or very odd linking patterns such as 100 links pointing to only main domain with 1 anchor. For most part almost all had less than 20 poor links likely from sources like pingbacks.
7. They for the most part do not seem to meet the quality guidelines set forth by google. Most had 98%+duplicate content and no authority to rank it.
Things that wont get you deindexed:
1. .infos – while google does seem to offer less authority to these domains to start with, they are fully capable of doing well and getting the authority you need to do well. There is somewhat of a guilty until proven innocent thing going on with .infos though. i ran a test not too long ago for a very low competition niche, the exact match .com was able to get to bottom of page 1 after 5 weeks with no work while the .info achieved the top of page 2 after same time period, both used exact same cloned site, were on same ip and had same seo and backlinks which was basically none. This doesnt prove anything but it was enough for me to buy more .coms when i could. on same note i likely could have outranked the .com with maybe 5 minutes worth of backlinking and seo work.
2. your host, its highly possible that google has targeted coolhandle simply because its IP’s/subnets have been found to host a high number of either low quality or and therefore looks a little deeper, BUT this alone isnt going to get you banned if your not doing something google doesn’t like. I am sure coolhandle is fully capable of hosting high quality sites that do extremely well, this goes for hostgator and any other providers as well.
3.duplicate content. I have plenty of sites that use nothing but duplicate content, and have very high domain authority and very good traffic. Its very easy to rank duplicate content from mage, or plr as long as your site has the needed authority. Without authority your simply not going to rank, and thus you wont get traffic, but its not going to get you deindexed. This being said a site that has very low authority and very high level of duplicate content is subject to atleast filtering, which means google will filter the results leaving your pages either ranking extremely low or not at all. That being said a certain level of unique content is always good.
4.your IP – ive seen a number of cases involving mage clients of mine where some of their standard mage sites had been deindexed on one ip and other higher quality sites were left alone. As long as your site is worthy of being in the index its fine, but go under googles radar and you’ll likely get reviewed harshly so plan on getting bombarded with bans if your building every site the same as the one that was deindexed.
The most obvious thing i noticed though was a lack of domain authority and quality content which is enough considering google quality guidelines. It is possible to get a site reindexed although very unlikely. http://www.google.com/support/webmasters/bin/answer.py?answer=35843