Using GUIDs

Hi list!

I'm currently thinking about using GUIDs as primary keys. To be more
precise: On *some* of the tables in my structure I *will* need GUIDs (or
UUIDs or whatever format may proove usefull). Now, this implies that
using a bigserial-field for readability and the uids is redundand, so
I'm thinking of dropping my current primary-key-columns in favor of an
uuid-column.
In the postgres-docs I can't find any built-in data-types directly
supporting guids. I found the project pguuid on gborg but it somehow
lacks documentation and doesn't seem very promising (since it doesn't
seem to be touched since three years ago...).
I have found some older discussion on the archives but in the end noone
ever came up with THE solution nor did anyone talk about the
performance-impact using a guid-row as primary key would have over
using, let's say bigint.
Has anyone made some test in this field and can share some experiences?
Would this question be better placed in the hackers list?

Best regards

Dennis