Google On Pages Popping In & Out Of The Google Index

Google has spoken about being on the edge of indexing is similar to Google thinking those pages are on the edge of quality - they seem to go hand in hand. If Google does not deem the page to be high quality enough to be indexed, it won't be indexed. John said the other day that it is common for a page to "pop into the index for a bit, and then pop out again."...