The ADO.NET team blogged about it a month ago but I just saw it. In .NET 4.0, the System.Data.OracleClient will be deprecated. It will still be there and apps using it will still work but warnings will be generated at compile time but no errors will be generated at runtime.
So what do you do if you used this provider? Well, keep your app as is, it will still work, or change the provider for the Oracle one or for a third party one.
Oracle : http://www.oracle.com/technology/tech/dotnet/msoc/index.html
DataDirect Technologies : http://www.datadirect.com/index.ssp
The Oracle one (Oracle Data Provider for .NET) is available for free. Lets hope it will stay free ;-)