The usual newbie licensing question...

Note: I've read http://www.gnu.org/licenses/gpl-faq.html before posting,
but I am still confused...

Hello,

please bear with me, I am not a developer by training nor by profession,
just a spare-time mostly-for-scripting-user of Python. This set of tools
looks just too great, so it may be that I will use it to try to build one
or the other tiny application for my employer's customers. We're a small
engineering/consulting company in the railway industry, and organising
workshops is one of our main activities. That much for the introduction.
Now to the actual subject:

If I build an application for a customer using GNUe (but without touching
the source of GNUe itself), does this application fall under the GPL just
as GNUe itself (that's the way I understand GPL)?

I wouldn't mind making the source freely available myself (as this will
probably give some feedback by more experienced people than myself and thus
teach me lots of new things), but maybe a customer won't like having to pay
for something (actually for my time while I'm doing it) when afterwards
their competitors can just get the same thing that they paid for for
free...

TIA,

Best regards,

Wolfgang Keller