People using Parallels to virtualise Windows will see a boost in 3D graphics performance thanks to support for DirectX 9.0, DirectX Pixel Shader 2.0 and OpenGL 2.0. The new Adaptive Hypervisor automatically shifts system resources around between the host and client operating systems to optimise performance, while you may allocate 8GB of RAM and up to an 8-way CPU to Parallels. The company claims a 50% performance boost over previous versions.
The company also did some visual tweaks, such as adding a feature called Modality, which - as far as I understand from Parallels' website - means you can get an overview of all your virtual machines using Expose. Coherence has been updated as well, so that Windows programs are added to the Mac OS X dock when you switch to Coherence mode. You can also manage your VMs from your iPhone.
Verson 4.0 is available now for USD 79.99, with upgrades USD 39.99. Users who purchased version 3.0 on or after 1 September 2008 are eligible for a free upgrade.