95% drop in number of pages indexed

Recurring issue and spikes with google indexing

[mluggy]

We run a community-generated-content website around textual summaries and short articles written by users.

For the 4th time, Google had dropped 95% of our pages although it constantly spider our site through normal crawling sessions and sitemaps.

The following is repeated monthly:
1) Number of pages start raising in 200-500 per day
2) Number of pages reaches around 20,000
3) All of a sudden, a sharp drop to 900 pages
4) Daily drop of 40-50 pages per day up to around 600 pages

More info:
1) New unique articles are written in a rate of 600 per day.
2) Site is alive for 18 months
3) Site is indexed very well by other search engines
4) Site is ranked well for the remaining pages in Google, even for highly-competitive phrases

Anyone had experienced this?
Thank you!

Michael

[edited by: engine at 11:48 am (utc) on July 19, 2006]
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