The chaps over at TweakTown tested AMD Athlon 4850e & 780G as HTPC Platform:

It's clear that AMD has really been working on getting power efficiency on its processors and chipsets to a point that they are in direct contention with the competitors. In fact, AMD has the most power efficient chipset available on the market so far with the 780G. A 4850e based HTPC is really worth your investment. AMD's Hybrid graphics has been what I would call a moderate success. While we have only used a rather low powered discrete GPU in conjunction with the onboard HD 3200 GPU, adding in something like a 3600 series GPU would result in far better gaming performance, but power usage would go even further up on the scale, as would heat generation. Considering we only had one fan running in low power mode on this system, its acoustics were extremely easy to tolerate. In contrast it was not the dominant background noise in the entertainment area.

As for AMD's latest Athlon 64 offering, the 4850 for all its low power draws puts out some serious calculations. At 2.5GHz it's a definite high powered monster for a HTPC. No video playback was lagged, and load times with Vista Home Premium were right on what we would expect for a system with this hardware configuration. In fact, its load times were the same as a Phenom X4 clocked at 2.5GHz. Overall, the AMD HTPC/low cost PC is what we would consider a success for light gaming or digital home storage. It's nice to see AMD cover the CPU market from different angles.