I've been contributing to the Scala compiler project , focusing recently on its .NET version. We're not yet using CCI but a custom-developed metadata solution. But we all spend some quality time with CIL one way or another.
The Scala team participates in this year's Google Summer of Code , where students get paid for contributing to open-source projects. I hope you also find interesting challenges at the Scala project ideas webpage, http://www.scala-lang.org/gsoc2010
From that list, the following are directly related to .NET technologies:
6. Scala Test Suite on .NET
9. A new backend for the Scala.Net compiler to generate C# sources
12. Adding LINQ-awareness to Scala.Net
Your ideas are welcome! For example, here's one more: 
If you know students interested in compiler stuff, please let them know about these projects.
 The Scala Compiler Corner,
 Google Summer of Code 2010 http://code.google.com/soc/
 Scalify.NET and joint compilation of Scala and C#,