updates either go on daily or there are multiple indexes being shown. Here are my daily stats for the last couple weeks. These are the number found when doing a site: command and then clicking on similar pages for the domain. The most recent is at the bottom. 8,800 8,980 8,830 8,450 missed 9,100 9,110 9,000 8,980 9,100 8,860 8,860
I don't think there will be a dance per se, I got the impression at Pubcon and SES that the day of the montly updates are over for both Google and Yahoo. Yahoo will be adding sites continously and refreshing SERP's all the time. As to backlink updates, that's yet to be seen.