I had a reporting question come up today. Let's say that you wanted to get a report of Accounts with Opportunities but only those with a specific Record Type. For example let's say you had the record types Donation, Grant, and Major Gift. How could you get a report of Accounts which ONLY had Grants and NONE of the other types? If you just filter on record type = Grant you'll see Accounts that have Grants plus those with other types as well. Btw, this isn't the exact scenario I have but is a close analog to the actual use case (which involves custom objects but a similar data relationship).
