While I have not implemented partitioned views in porduction I have done some experimenting with them. I believe that if you are using an Identity field in your tables that affects how they work when part of a partitioned view. What I read in BOL and elsewhere is that you should not use and Identity field in the base tables and that your partitioning column, in you case client id, should be the first column in a composite primary key.
I have always used stored procedures to do updates and you could do that using the client id as a parameter to determine which base table to update. Then you could still use the partitioned view for reporting. The code would be something like
If client_id = 1
You could even have separate sp's per base table that are called from a central sp, which would keep the sp from recompiling when you passd in a different client id.