When server moves from 10.2.0.4 to 11.2.0.3.4, will clients have to do so, 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. (finally I found some back again)

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