Has anyone used either :-
"Oracle PL/SQL For Dummies (Paperback)"

or "Beginning PL/SQL: From Novice to Professional (Expert's Voice in Oracle) (Paperback)"

If so what did you think? Do you have any strong thoughts?

I know SQL pretty well and a very little PL/SQL.

Given you are already comfortable with SQL, I would just suggest picking up a copy of SQL in a Nutshell: A Desktop Quick Reference; it covers, not only Oracle, but also MySQL, PostgreSQL and SQL Server.

I am not quite I am sure about why that would be a good idea. SQL and PL/SQL are quite different.
http://en.wikipedia.org/wiki/PL/SQL

"PL/SQL (Procedural Language/Structured Query Language) is Oracle Corporation's proprietary procedural extension to the SQL database language, used in the Oracle database. Some other SQL database management systems offer similar extensions to the SQL language. PL/SQL's syntax strongly resembles that of Ada, and just like Ada compilers of the 1980s the PL/SQL runtime system uses Diana as intermediate representation.

The key strength of PL/SQL is its tight integration with the Oracle database."

If the current version of the O'Reilly book is as good as my old copy, highly recommended.
http://oreilly.com/catalog/9780596009779/