System.Data.OracleClient 在将要发布的.NET Framework 4.0中还会保存，但会标记为“不赞成”，这对现有的程序没有影响，但如果你用.NET 4.0来重新编译你的程序，你就会发现出现大量的Worning.
我们推荐我们的客户们去使用我们合作伙伴的ADO.NET Provider for Oracle,不要在使用微软现有的OracleClient。

---注：意思很明显，微软将不会再OracleClient上投入更多精力来更新版本了，而是交给了社区和合作伙伴，有点令人失望，我们有大量的程序都是基于OracleClient，根据社区的反应ODP.NET 不太稳定，问题多多。

不过看Oracle自己的网站上的对比，ODP.NET确实功能比较强劲，加以时日应该能成为主流

这么重大的事件，我居然才知道，看来确实孤陋寡闻了！
英文原文:
System.Data.OracleClient will be available in the upcoming 4.0 release of .NET Framework; however, it will be marked as deprecated. This will have no impact to existing applications and these applications will continue to work as expected. Developing new applications which use OracleClient will be supported; however, warnings will be raised if the applications are compiled against .Net 4.0. Once compiled, no warnings or errors will be generated while running these applications. We strongly recommend customers to use our partners’ ADO.NET Provider for Oracle instead of continuing to use Microsoft’s OracleClient for new application development.

Microsoft will continue to provide hotfixes for critical issues in System.Data.OracleClient as per the standard support policy for .Net Framework 4.0. We will also continue to make critical bug fixes in future service packs for .Net Framework 4.0.

Thank you,

Himanshu Vasishth
Program Manager, ADO.NET OracleClient

http://blogs.msdn.com/adonet/archive/2009/06/15/system-data-oracleclient-update.aspx