Our recent conversion from SQL Server 2000 to SQL Server 2005 revealed a couple of issues with stored procedures that run BULK INSERT commands.  [These issues were not issues with under SQL Server 2000.]

1.  "Operating system error code 5(Access is Denied)" when attempting to execute this command using Windows Authentication.  This appears to be an impersonation / delegation issue that we believe we can fix with delegation.  [Stay tuned ...]

2.  Assorted format file errors "Invalid destination table column number ...", "Bulk load data conversion error (truncation)", etc.  We've been able to workaround these by increasing the column widths for some of the column definitions.

The moral of the story is to test everything that calls a BULK INSERT carefully as part of the upgrade process ...