I was the original author of the wiki Outlook PST Import Wizard Tips.

Back in 2006, even if you modified the import wizard registry entry to allow attachments over 10MB, you still had a memory issue on the ZCS server that would prevent messages with large attachments from moving over if the server had a non-massive amount of RAM.

Do the current migration tools for exchange have issues migrating mailboxes with very large attachments even with the registry key set? I'm thinking of migrating exchange mailboxes containing messages with 30MB - 50MB attachments.