One of the things that I've worked on for the past while is a Quartz backend for Cairo -- mainly for Mozilla, but also to show that Cairo has a great API that maps well to existing 2D APIs.  Cairo is a great 2D portability layer, ensuring that rich 2D graphics can be portable.  I'm excited about the upcoming Cairo 1.6 in particular, because the Quartz backend will be marked as stable and supported.  This will mean that Cairo is usable and supported on the three main platforms in use today -- Windows, Linux, and MacOS X.  I've filed a bug with Apple (bug #5802204) about making public the APIs that I've had to use to implement the full suite of Cairo capabilities using Quartz.  (For anyone interested, the cairo-quartz implementation file has a handful of quite useful methods.)

One interesting bit of fallout from this is that Quartz/CoreGraphics also happens to be the native graphics layer for the iPhone: so, Cairo is trivially portable to the iPhone.  The major issue is that Cairo currently uses ATSUI for font access, whereas it needs to be using CGFont -- which is the native font API suppored under MacOS X 10.5 and the iPhone.  (However, the CGFont API is missing many public methods to make it entirely general, but I hope that will be remedied in time.)  I've made some last-minute changes to Cairo to allow us to switch to a CGFont-based text backend with no change to Cairo-using apps, and I have such a backend in progress for landing shortly after Cairo 1.6 is released.

There is also some exciting work going on with improving the pixman library that cairo uses for its software-only rendering -- I've often maligned it for being slow and hard to work with, but the newer cleaned-up version is much easier to deal with, and Soeren has great plans for its future.  A number of people are working on adding highly optimized MMX and SSE2 compositing routines to augment the little bit of MMX code that's present currently.  Initial benchmarks are pretty encouraging, and I'm hoping that we can do some optimization work targetted at ARM as well.  There is also some work in progress to implement accelerated backends using OpenGL (and ultimately Direct3D).

Gecko 1.9 (and thus Firefox 3) will be shipping with Cairo 1.6 (or, as close as possible, if the schedules don't quite line up): everything that Firefox 3 renders on the screen is going through Cairo, and is ultimately translated by Cairo into the native platform API.  Future work to expand Gecko's graphical capabilities will intimately involve Cairo.  It's safe to say that Cairo is ready for prime time.