Was this a particularly big PST file?
I think it is to do with Outlook not releasing the memory when chunking up the PST files to the Vault server.
For every 10MB chunk Outlook does not release this until Outlook.exe is consuming a huge amount of memory and things bottom out.
I believe this is an Outlook 2003 flaw and apparently should be resolved in Outlook 2007 as this releases the memory associated with the chunking process.
You might be alright if it is for a few users because of the relative advantages of WAN links and prepopulation of the Offline Vault etc.
I would use the Locate /Collect/Migrate functionality if you can.
Hope this may help.
