I downloaded the latest git snapshot to give it a try. Here are my results:

1) In the debug build (ECL_DEBUG = 1 in Makefile) ECL code can't be stepped through from the Visual Studio debugger anymore.

2) si_safe_eval(3, form, Cnil, evalErrorSymbol) evaluates the form, but always returns evalErrorSymbol. cl_eval(form) seems to work normally.

On the positive side:

1) Lispbuilder-sdl and cl-opengl compiles and runs with ECL (ECL could always load these libraries, but couldn't compile them until now).

Note: I didn't try the latest versions of those libraries, and I had to manually do a lot of massaging of lisp files in those packages, such as breaking long lisp files into smaller ones, due to the 64kb limit on strings enforced by the MSVC compiler. One long lisp file consisted of a single call to the cffi function defcenum, so I wrote defcenum-append to continue the definition of a c enum in another lisp source file.

2) The multithreading feature works - I can alter forms while other threads are running. This is awesome.

My current fallback build:

The build which I already have and works well for Win32 MSVC ECL embedded work is the June 29th 2009 build.