I am looking for a formula to use in a validation rule that would restrict users from changing the value of our Account type field to any Partner related value.  Ideally I'd like only certain users to be able to change the value.  I came up with this one but it doesn't work:

AND(
ISCHANGED(Type),
OR(
ISPICKVAL(Type,"Partner -- Bus Dev" ),
ISPICKVAL(Type,"Partner - Consultant" ),ISPICKVAL(Type,"Partner -- Distributor" ),ISPICKVAL(Type,"Partner -- Inactive" ),ISPICKVAL(Type,"Partner -- Pending Paperwork" ),ISPICKVAL(Type,"Partner -- Referral" ),ISPICKVAL(Type,"Partner -- Technology" ),ISPICKVAL(Type,"Partner -- VAR/Reseller" ),ISPICKVAL(Type,"VAR-IT DISTI" ), ISPICKVAL(Type,"VAR-PA DISTI" ), ISPICKVAL(Type,"VAR-IT" ), ISPICKVAL(Type,"VAR-PA" ),ISPICKVAL(Type,"DISTI-IT" ),ISPICKVAL(Type,"DISTI-PA" ),ISPICKVAL(Type,"ISV" ), $User.Username <> 'XXX@imprivata.com', <> 'XXX@imprivata.com',$User.Username <> 'XXX@imprivata.com')

Any suggestions?