We are in the process of selecting a workflow solution for a company that uses Microsoft products end to end. Given the news on WF4, in that it seems to be essentially a rewrite
Haiving just launched a project which .NET 3.5 and workflow I'd say that the current release of WF is good enough to use and run with. It has helped us to get a product out quickly (we have the usual feature creep and requirements changing weekly). However, I have a list of complaints with it:
I like the ideas and potential of Workflow based development, however I am not in a hurry to repeat this experience and would probably stick without it for long running processes. One place I would use it again would be in a short, complicated process (like a rules engine for working out prices).
Another point to use the current version is that "Dublin" (Microsoft new App Server) will be built on WCF & WF .NET 4.0 but will gladly host 3.5 WF's. So you will be able to migrate to that without a rewrite.
Maybe it is a little late for you, but now that WF 4.0 is released in beta, other people thinking the same question can consider backing the 4.0 horse instead of 3.5 horse.
This goes some way to fixing the following problems:
•The workflow designer will drive you insane because it is so slow (in certain circumstances) and re-arranges your state machines as it sees fit. [Designer Perf Improved]
•Its not easy to unit test them. There are ideas out there but none seemed particulary easy when we started this WorkFlow Unit Testing [I think it's a little easier now, some of the introduction to workflow samples include plenty of unit testing]
Just a quick note to mention that Visual Studio 2010 CTP contains a new updated WF designer as part of the Oslo objective.
I, as a workflow developer, think that current version is painful to use. This is not surprising as this is a v1.0 software out from microsoft :)
I think you should first consider your expectations from a workflow software. Do you have a well defined list of expectations from WF? Acutally I am wondering content of such a list. Maybe we can help more detailed on each topic.
My understanding is that Microsoft will provide backwards compatibility and/or a migration strategy to the new WF, so I would guess that you are safe to use it. However, I have heard from other developers in my organization that the current version of WF is extremely painful to use. If you have the budget (and depending on the complexity of your workflows), you may want to consider K2: http://www.k2.com/en/index.aspx