Following features can be enabled by Salesforce.com Customer Support:
(a) Organization Administrators Can Login as Any User:
Login option associated to each User under “Manage Users” section. You need to contact Salesforce.com customer support to enable this feature. Read more...
(b) Active Lookup Filters:
In each object of Salesforce we can have lookup filters. It can be “Required” or “Optional”. You can create “Optional” lookup filters as many as you want. BUT you can ONLY have 5 “Required” lookup filters on an object. You can contact Salesforce.com customer support to enable it up to 10. Ten (10) is the maximum limit of “Required” lookup filters on an object.
(c) Audit / System Fields: