As I mentioned earlier (see Performance Comparison: Rectangular Array vs. Jagged Array) I ran the same set of tests in .Net framework 2.0 (Beta 2) and the results are still pretty similar to that in 1.0. I would suspect that the test results be similar in the final product of .Net 2.0.
While I mentioned that the performance of the jagged array is better than rectangular array, I guess we need to put this conclusion in context. That is, if you are mostly doing sequential access to the arrays.
An article on MSDN magazine (see Harness the Features of C# to Power Your Scientific Computing Projects) suggests that the performance of jagged array actually degrades significantly when accessed randomly. A scenario that would fit this case is the operation of sparse matrices.