The Ibis web page
http://www.cs.vu.nl/ibis/publications.html
contains links to various Ibis papers.
The best starting point might be
http://www.cs.vu.nl/ rob/papers/cpe03.ps.gz
, which gives a high-level description of the stucture of the Ibis system.
It also gives some low-level and high-level benchmarks of the different Ibis implementations.
The docs/api subdirectory of the Ibis installation provides documentation for each class and method in the Ibis API (point your favorite HTML viewer to docs/api/index.html in the Ibis installation). The Ibis API is also available on-line.