The latest is DogDog made mass changes to page titles and meta tags. Again, Google temporarily removed his site for his chosen search terms. A day later, he reversed all the tags and titles, save one. Google re-indexed the site at 6 and 27. It happened, because the site is now being seen with less "trust" seo factors than before. The site appears to be going through massive changes at a time. and Google sees this as a website, which can be counted on less for reliable and useful reliable content for it's users.

Yahoo is still out on re-indexing the website for one of the search terms. The lesson here is if you want to keep being indexed, stop making mass changes to your website all at once. There is no need for it. All it looks like, is your website is going through radical changes far past what Google's algorithm will accept as "progressive" change. And if it is "radical" change, you can expect Google to act much as a bank would for anyone of it's lending clients. Once you start respecting your website in the same manner you respect your company's credit rating, you will be in a far better position to make changes to your website in affecting control over your indexed positions in any search engine.

So further to the above, mass change is all about brute force tactics. Anything which is outside the development of all websites indexed within a search engine, will be flagged for further analysis by Google, and will be checked for all machine build practices. If anything you have done is not within the "natural" developmental nature of website development, you can expect search engines in general to respond unfavorably.

Your website is a breathing entity and once you realize it takes constant daily care and making changes are always required, you will at least be able to climb in indexed positions and keep them over time long term. Build to last is not the same as build over night. One is a pirate approach, the other an investment approach. I'm sure everyone can understand the outcomes to both methods.

Use automation of course, just only enough to look like you are building by hand. This is the key. Automation should be working just as if you had someone hired to so the work. If you design and program your software accordingly, you will succeed and not alert search engines to flag your site.