When using Oracle, you absolutely have to use placeholders. Anything else will completely kill your scalability.

The only time I have ever had performance problems with placeholders is when this caused the execution plan (which indices to use and so on) for the query to become inefficient. This can happen if the data is very "skewed": If you use placeholders, Oracle cannot take the actual values of these columns into consideration and has to assume "average" data points. If you have, for example, a table "employees" and 95% of them are male, and then have a query for only female employees, not using a placeholder for the gender might actually be beneficial. Another example would be a limited query (return just the first x rows) which can possibly create a better plan if "x" is known at preparation time.

However, this should happen only in very rare cases. If you can consistently reproduce this problem, contact your DBA to find out what execution plans your query creates.