Featuring Qt Platform Abstraction, threaded OpenGL support, multithreaded HTTP and optimized file system access, Qt 4.8.0 can be downloaded as binary or source packages (Qt Download Page).
The threaded OpenGL support would be nice to see if integrated into the mapper (even for 2D). The optimized file system access is really interesting to me - hopefully it'll improve on Mudlet's startup time (+ profile selection, and profile loading), which is not the quickest