inheritance vs performance

Hi,

I'm wondering if there could be problems related to inheritance in the
following scenario (with PostgreSQL 7.4.1)...

1 A-table, abstract.

Max 10 B-tables that inherit from A, with sometimes some more columns
than A. These are also abstracts.

"n" C-tables that inherit from 1 B-table, without more columns.
Each C-table could contain quite a lot of rows (500K, 1M, ...).

Could there be problems, or performance issues, related to inheritance
if there is "too much" C-tables (in combination with the number of
rows)? And what would be that "too much"?

Remarks:
A-table could be removed as it's not that important/relevant.
The purpose of this structure is not to be able to easily select through
the parent in all children tables, though it would be appreciated.
The purpose of this is just to be able to easily create C-tables, and
maybe also to easily handle structure changes of A or B-tables.
The master words here are "performance" and "reliability".

Thanks,
Pascal