About a week ago I got one of those dreaded messages from Google saying that 'my pages do not conform to their guidelines...' Sure enough, there were some doorway pages there (leftover from a SEO company from about 7 years ago, that I simply forgot to remove). The whole site was totally gone from the index.
I deleted the offending pages, submitted request for re-inclusion, and got prepared to wait for a few months - but surprise - the site was back, fully indexed in 5-6 days. Not bad.
Another fact I found interesting. This is a commercial site. The traffic dropped to about 40% once I wasn't in the index. However, the number of orders I received during this time did not drop at all. I always assumed that Google was bringing in good highly convertible traffic. Maybe not?