Exchange Digital ID's vs Thawte ID's?

["Mark G. Spencer" <mspencer () evidentdata com>]

I have recently been asked about authentication and encryption options for
Microsoft Outlook (and sometimes Exchange) users.  The three options as I
now see them are:

1.)  PGP
2.)  S/MIME Digital ID from Thawte (or other CA's)
3.)  Exchange created Digital ID

For now I am focusing on the comparison between using a free Digital ID from
Thawte and an Exchange created ID.  Could someone explain the tradeoffs
involved with going with one or the other?  I'm assuming an ID issued from
Thawte is more useful than one created via the Exchange server because it is
more "universal" and you can administer ID/Certificate features through
their website?  Also, for users who do not ever connect to the Exchange
server, the ID from Thawte doesn't rely on Exchange in any way, another
benefit?

Thanks for the advice,

Mark