People have been wondering for a while what the future of WF3 was since the release of WF4. So far both workflow stacks have coexisted in .NET 4 and there has been no official statement about the future of the older WF3 stack.
That has just changed!
The workflow team at Microsoft has just announced that they are marking the WF3 stack as deprecated with the next release of the .NET framework, .NET 4.5.
Of course the types are still there but you will get compile time warnings for using them and you can expect the classes to be dropped some time in the future.
“Warning BC40000: X is obsolete: ‘WF 3 types are deprecated. Please use WF 4 instead.’”
So if you are sill using WF3 this is a good moment to invest the time and start learning Wf4.
You can read the official announcement here.