You are totally right, it had been a while since I had looked into this. I was confusing (blending together?) pyinex and IronPython. You are right, IronPython (and tons of other languages) all have access to the .Net libs, but pyinex is what I was thinking of. Apparently, though, it is not fully developed yet.
I was thinking you were going to refer to .Net linking with Office, which seems to be something different from the COM automation, and more complicated than I've ever been interested in.
That, however, looks pretty darn cool. On the odd occasion I've used Python/COM/Excel together, I've really wished for a Python shell inside Excel to do things like:
for cell in Range('a1:a10'):
cell.Value = cell.Value.split('-')[0]
or whatever. I don't know if Pyinex will quite do that, but thanks for the link!
You can do almost exactly that in Resolver One (http://www.resolversystems.com/), which has got a Python console as well as allowing Python functions and Python syntax in the grid. It's a separate spreadsheet program, though, not an Excel plug-in.
Alternatively, there's PyXLL (http://www.pyxll.com/), which lets you write Excel user-defined functions in Python, but doesn't have a console.
http://code.google.com/p/pyinex/