The Wine 1.4 release comes just one day after CodeWeavers released CrossOver XI, which is their latest major step in their commercial-based Mac OS X / Linux software for running Windows applications. CrossOver XI is based on the Wine 1.4 code-base.
The 1.4 release announcement mentions, "The main highlights are the new DIB graphics engine, a redesigned audio stack, and full support for bidirectional text and character shaping. It also contains a lot of improvements across the board, as well as support for many new applications, notably Microsoft Office 2010."
On the graphics side, the Device Independent Bitmaps (DIB) engine is a huge improvement for many applications, Wine also now better uses the X RENDER extension, there is now support for multi-sample anti-aliasing (MSAA), an improved blitter, support for v-sync / swap intervals, performance improvements, OpenGL extension handling improvements, the DirectDraw implementation is much better, and the D3DX9 shader assembler is nearly finished.
There's also the completely re-designed audio stack that's drived from Microsoft's Windows Vista audio model (with re-written ALSA/OSS/CoreAudio drivers), support for animated mouse cursors, better internationalization, GStreamer support for audio and video playback, and support for system tray notification balloons. Again, see the release announcement for full details.