I don't have solid evidence, but I think that if a webmaster makes changes to the titles and description meta tags of several pages at the same time, those pages might get sandboxed.
I did a sitewide edit of keyword and description meta tags on a site about 2 weeks ago. This is a very large affiliate site. Hundreds of thousands of pages. That site is still ranking quite well in the SERPs today.
[edited by: ssjxxx at 4:48 pm (utc) on Dec. 16, 2005]