It would be nice to be able to run queries, filtered on the results of comparing two date fields. e.g.:

Contact[] contacts = [SELECT id,
name,
member_status__c,
last_update__c,
renewal_date__c
FROM Contact
WHERE member_status__c = 'Active' AND renewal_date__c < last_update__c];

(This could also be used in setting the flters/criteria for views and reports)