JSIL is also great, but its philosophy is that yo write .net code and run it in the browser, whereas Saltarelle's (and Script#'s) is that you write Javascript but with better tools. Also, the script that JSIL generates is very far from what you would write by hand, whereas that generated by Saltarelle/Script# can be distinguished from hand-written script primarily because the indentation is always correct and there is never an accidental loose comparison operator.

Could you not somehow reuse the JSIL code generator, and add things for the approach you took in Saltarelle (good integration with JQuery etc.)?

Another question, did you do any performance comparisons of Saltarelle? (to normal C# builds, to JSIL, or anything else?)

I think the tools fill different purposes, so integration with JSIL is absolutely a possibility in the future. I did not do any speed comparisons, I just translate what you write in C# to the equivalent script, so if you write a fast script it will be fast, if you write a slow script, it will be slow :)

Well, how you create data structures might matter for performance - if you turn C# structs into JS typed arrays for example and do the proper conversions, that could be much faster than simple JS objects or even arrays.