While the AMD Radeon HD 7000 series graphics cards have been out for one year now, the open-source support has been shoddy. AMD was fairly quick in delivering kernel mode-setting support, but the 3D bring-up has been slow. There were significant architectural changes to the GPU between the HD 6000 and HD 7000 series hardware, which necessitated the introduction of a new Gallium3D driver called RadeonSI, but for end-users simply wanting their hardware to work on open-source software, it's been a damn slow process.
Everything is technically there for the past few months but it's been bug-fixes and implementing other changes/features that is still an ongoing battle as the Radeon HD 8000 series launch approaches. It's been a mess but at least the forthcoming Radeon HD 8000 series won't be another big architectural overhaul to the Radeon family. In terms of the open-source 3D coverage, basic OpenGL demos should work but at last check any of the advanced OpenGL games/applications were still a wreck.
The 3D bring-up is also important for the Southern Islands GPUs since AMD is now exclusively using 2D acceleration via the GLAMOR library for new hardware. This means in order to have 2D acceleration, 3D/OpenGL is required. Some fixes landed last month and now Michel Dänzer has pushed two post-Christmas xf86-video-ati GLAMOR changes.
The second commit today by Michel, which is mostly deleting about two-thousand lines of code, is entitled glamor: Enable full 2D acceleration for SI as well. For now though if you are a Radeon HD 7000 series owner, you are best off still using the proprietary AMD Catalyst driver on Linux until the power management, video acceleration, OpenGL 3.x/4.x, OpenGL performance, and other features are sorted out.