When you run a crawl on a Windows SharePoint Services 3.0 site, the crawl lasts for several days. This problem occurs when there are approximately 220 or more index files, and the index files are not being merged.
To resolve this issue, apply the following updates:
975002 Description of the Windows SharePoint Services 3.0 Cumulative Update Server Hotfix Package (Sts-x-none.msp): October 27, 2009
975731 Description of the SharePoint Server 2007 Cumulative Update Server Hotfix Package (Coreserver-x-none.msp): October 27, 2009
Note This update works in a SharePoint Server farm environment, but this update does not work in a SharePoint stand-alone installation.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.