inheritance performance

Wondering ...

From a performance standpoint, is it a bad idea to use inheritance
simply as a tool for easy database building.  That is for creating
tables that share the same columns but otherwise are unrelated.

For example, let's say I have the following set of columns that are
common to many of my tables.

objectid       int,
createdby      varchar(32),
createddate    timestamp

... and let's say I create a table with these columns just so that I can
then create other tables that inherit this table so that I have these
columns in it without having to respecify them over and over again
separately for each table that contains them.

From my understanding, all the data for these columns in all the child
tables will be stored in this one parent table and that, furthermore,
there is a "hidden" column in the parent table called tableoid that
allows postgres to determine which row is stored in which child table.

Given that, is there a performance hit for queries on the child tables
because postgres has to effectively put a condition on every query based
on the tableoid of the given child table?

In other words, if say child table A has 10 million rows in it and child
B has 2 rows in it.  Will a query on child table B be slowed down by the
fact that it inherits from the same table as A.  I'm sure the answer is
absolutely yes, and so I guess I'm just looking for corroboration.

Maybe I'll be surprised!

Thanks a bunch,

Ken