WOW!
Didn´t think I´d get so much helpful feedback so fast.
Thanks for all the insights and personal experiences.
Now I am really confused - but in a good way! I thought most of you would tend to lean towards XSI…
I really like what I know about Messiah! The workflow, the easy and precise rigging, the animation tools (as far as I have used them) and the feeling one has while working with the UI. Even though I have “used” it for about a year I feel still like a newbie, since I only have very little time to experiment.
I have always thought about using just Wings3D (or another modeller) and Messiah, but I find the way of the “In-line documentation” does not get to me… I like to have a book or guide to read while working or even learn/study without sitting in front of the PC. Call me old fashioned, I just can´t help it. So I guess thats why I still don´t know much about the render engine, although I already upgraded my M:A to Studio Wks half a year ago…
Joe Cosmans CDs really got me started with rigging; those tutorials are well structured and clean - they even get you into the “Messiah flow” and that is where the fun really starts. So I will go over his CDs for animation next and hopefully Tarons tutorial(s) for rendering soon, to actually see what I do… 
vjholofx and rush123: thank you for the insight from an XSI-users point of view. As I tested XSI a few weeks ago, I had just the same impression, although I liked the way the user moves around in the program, I felt that it is so huge and complex that it almost repelled me. So I guess I will postpone my decicion concerning what pipeline I will setup and stick with Messiah for now.
Wegg: I imagined that you were using just Messiah, and I really like your work. You (and your work) are actually the reason for thinking about using Messiah only. I printed out the chm-manual and actually learned way faster than before, reading it while using M. The only drawback now is, that it is really hard to find specific topics.
I believe that Messiah could actually get a lot more attention from 3D-users everywhere, if the documentation was available as a well structured PDF/printed manual. The writing style in the chm is quite enjoyable, but sometimes the structure in chapters gets the reader confused. I´d really like to offer PMG to work on a concept/layout for their manual for free, if the timeframe is loose enough. I do quite a bit of writing in my job as copy-writer/account-executive/medical advisor in a large German healthcare-agency. My wife is a professional designer, and she offered to help me with the layout part. We could use the existing chm-texts as a base and go from there. Do you think PMG would be interested in this, even though my experience with the program is limited? I really like the program and believe that there will be a successful future for it, if some of the stumbing blocks for new users can be removed.
Thanks for your feedback so far and I would like to hear even more experiences of other users on how M:S is used in their pipelines.
LX