Primary Key vs Unique Key

I have used the data pump to migrate a bunch of paradox tables to interbase
and sql server 6.5

I just noticed that the data pump created unique indexes rather than primary
keys for the "primary keys" in the paradox tables.

Are there any performance penalties that I might pay if I leave these
indexes as unique, but not primary? I realize that I need to have a primary
key in the relational table if I want to reference it as a foreign key in
another table.  I also realize that primary keys cannot be null.  Assume for
the sake of discussion that the unique indexes are also not null.

Just wondering if anyone can save me some experimentation time.

-Jon Claney
Industrial Images, Inc.