Real World Lotus Notes Index Result in SharePoint 2007
Crawled Notes data: 1240 Gbytes
Crawled Notes Items: 2.7 Million
SharePoint Index: 70 Gbytes
SharePoint Search DB: 120 Gbytes
Data vs Index = 124:7 = 18:1, which is a ratio of 6%.
Index vs Search DB = 7: 12. Search DB is 160% of Index.
In total, (Search DB+Index)/Data=16%
Remember, this ratio varies in different environment, depends on how you use Notes Applications, how many attachments are there, and many other factors. I put it here only as a reference. Maybe update later.