Over the last several months I've seen a lot of reports about Outlook including the original invitees in the To field when forwarding meeting requests. If you or your users have this problem, see the following KB article:

The "To" field is populated with the original recipients of the meeting request, and the "Subject" field is not prefixed when you use Outlook to forward a meeting request that was responded to by the CDO application

Note that Exchange 2007 notifies the organizer (by email) when an invitation is forwarded by an invitee. This is not a bug.