primary keys

Hi Folks

I'm looking for a bit of advice regarding alpha primary keys.

I have a table (designed by someone else) that has a numeric primary  
key and also a unique non-null email address field.

The use of the primary key is causing me some headaches in that in   
multiple database server environment each server allocates a unique  
number from a range
(and that works fine) but when the table is replicated (master-master- 
master) the exception handling is a bit tricky because each database  
server may have
records that are duplicate at the email address field - with a  
different primary key number.

I don't know why it was done this way but it seems to me that the  
email addresses are unique, non null and could be used as the primary  
key. This would make the
replication much faster and simpler.

Does anyone out there think the change (number to email address as  
primary key) would be a bad idea ?

your thoughts would be appreciated.

regards
Grant