When server moves from 10.2.0.4 to 11.2.0.3.4, do clients have to, too?

First off: I don't find all the old topics of the Orcale support forums, like Database Administration etc.

Where are they? I gave thumbs down to the new interface.

Now my question: Our customer is moving from 10.2.0.4 to 11.2.0.3.4 and is asking what changes he has to watch for?

Do the clients have to move, too?

Was the password case sensitivity introduced in 11g or was it already with 10g?

Advice welcome,

Christoph