The lead (Mr Mickolov Wroussakov) of the project I'm currently working on has specified a custom namespace for all content schemas:

<xsd:schema elementFormDefault="qualified" 
targetNamespace="http://www.clientdomain.com/tridion/schemas" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns="http://www.clientdomain.com/tridion/schemas" 
xmlns:tcmi="http://www.tridion.com/ContentManager/5.0/Instance">

I was always under the impression that is is recommended to create a unique namespace per schema, here all of these implemented using the item shown above.

I don't see any issues as such, i'm just wondering if this could open up some problems in the future.