Bulk Change Distribution Groups to Universal

Exchange 2010 (and 2007 for that matter) requires all Mail Enabled Groups to be Universal.
This is because, unlike Global and Domain Local groups, Universal groups are replicated to GCs, forest wide.
It's pretty easy to convert them with PowerShell.

To bulk convert Global groups, run:

Get-DistributionGroup | where { $_.Grouptype -Like "Global*" } | Set-Group -Universal

To bulk convert Domain Local groups, run:
 
Get-DistributionGroup | where { $_.Grouptype -Like "Domain*" } | Set-Group -Universal

This has no change on Distribution Group functionality, but it does generate heavy traffic across the forest, so maybe run in off-hours.