Would you recommend Iron Ruby, Iron Python, or PowerShell for making a C# application a script host?
After some quick tinkering, right now I'm leaning towards powershell for two main reasons (note these a purely my opinions and if they are wrong, I'd love to know!!!):
1) It's simple to create a runspace with classes in your application; therefor it's easy to make your application scriptable. 
2) I've heard some rumors that IronRuby and IronPython are losing support from Microsoft, so they may be a poor long term solution?
As this is my first time adding scripting to an application though, I'd welcome all the advice I can get from people who have been down this road before.
Specifically, besides letting me know whether you agree with my two points above, I'd like to know if IronRuby and IronPython are much easier to use (for a user, not developer) than powershell, and if in your experience using the DLR is as easy as just passing an object to a powershell runspace? And if I added support for the DLR and IR/IP scripting would my application still be backwards compatible with XP?
I'm in a similar position.  I decided to use IronPython scripting but ever since I saw Anders Hejlsberg's talk "The Future of C#", I've had a feeling IronPython was doomed. 
It was in Microsoft's interest to get the DLR developed but they ultimately want us to use tools and languages they control.  After all, aren't you using C# and not Java?  So what will a Microsoft dynamic language look like?  How about dynamic, interpreted C# (Iron C#)?  Hejlsberg's talk made it clear it isn't that far away.  He even had a console window with a REPL interface.  That said, there's always a possibility for Iron VB.  Talk about closing the loop.
On the plus side for us programmers, Iron C# also solves another problem that I'm having trouble with -- the existence of two parallel object environments, one of .Net objects, one of Python objects.  It takes work to get from one to the other.  I assume an Iron C# would utilize the .Net class structure.
My advice: Stick with Iron Python and .Net classes.  When Iron VB or Iron C# happens, it'll be a quick, maybe automatic, language translation.  Besides, if enough of us use IronPython, Microsoft may change their mindset.
Would you recommend Iron Ruby, Iron Python, or PowerShell for making a C# application a script host?