I just noticed that we have published a couple of KB article about a new tool named Pre-Upgrade Checker which will ship with WSS 3.0 Service Pack 2. Based on the information in the KB articles this tool will allow you to verify if your current WSS 3.0 and MOSS 2007 site structure will be compatible with the next version off WSS and MOSS.

• KB 956201 - The LargeLists rule in Pre-Upgrade Checker for WSS 3.0 SP 2 can warn about large lists circuit breaker
• KB 956447 - The ModifiedWorkflowActionsFile rule in Pre-Upgrade Checker for WSS 3.0 SP 2 can warn that the default declarative workflow actions file was changed
• KB 956448 - The CustomWorkflowActionsFiles rule in Pre-Upgrade Checker in WSS 3.0 SP 2 can warn that custom .ACTIONS files exist in the farm
• KB 956449 - The ModifiedWebConfigWorkflowAuthorizedTypes rule in Pre-Upgrade Checker for WSS 3.0 SP 2 can warn that Web.config files contain modified authorized types for workflow
• KB 956450 - The CustomListView rule in Pre-Upgrade Checker can warn that customized list views that will not be upgraded
• KB 956451 - The CustomFieldType rule in Pre-Upgrade Checker in WSS 3.0 SP 2 can warn that customized field types will not be upgraded