Deprecation of TOM-based Event System
The TOM-based Event System is deprecated in favor of the TOM.NET-based Event System.
The TOM.NET-based Event System offers a more fine-grained and sophisticated way of catching and handling Content Manager events.
Also, it is not possible to use data in .NET that was obtained using MS XML (which is the case when using the old TOM-based Event System). Microsoft Knowledge Base article 815112 explains this issue: http://support.microsoft.com/default.aspx?kbid=815112
Note that calls to the TOM.NET API will no longer trigger old Event Handlers. The Legacy Pack for SDL Web 8.5 includes a Legacy Event Adapter to handle this.