For the information of whoever visits this page:
Raspberry pi does not have an official mono implementation on hard float operations. That's why a lot of mono stuff will NOT work, including xsp =]
A gentleman posted on raspberry pi forums an experimental version of mono with an implementation of hard-float which form me worked fine. The post is here.
For Arch Linux users, I've come up with a package build so that you can create an arch linux package, and posted on the same thread. Exactly here. Instructions on how to build it are also there.
Running xsp will work after this, at least for me it did. I also did use .NET to handle GPIO and all worked beautifully.
Hopefully this helps! =]