This is the longest gap we have had between Mono releases (1.1.15 to 1.1.16), but the wait was worth it. The inlining optimization is now turned on as well as a number of other small optimizations that enhance inlining and the results are excellent. Thanks go to Massi that tuned the optimizations and hunt down every bug until it was ready.
There is a lot of new stuff, in particular, Windows.Forms is better than ever in every possible way.
The full release notes are here.