The small form factor gaming/htpc market could be a good one for AMD, but they haven't been able to get any other companies to build them in volume. Usually you get the eeeBox or something underpowered using an E-350. Heck, HP is sticking those in full desktop cases which is absurd.
All the innovation left in the PC market seems to be on tablets and ultrabooks, not on the desktop at all. AMD hasn't pushed as hard on either form factor and it's hurt.
Also, why hasn't AMD done what nvidia did and become an ARM chipmaker? Tegra has sold well enough for nVidia and an ARM desktop box could be quite competitive in the next few years for the average user.