GPU mining is still not as decentralized, as basically only high-end PC gamers (with their own default cards) and the people specifically buying GPUs for mining will have a shot at it.
CPU-only mining would be a lot more decentralized, if such a thing is even possible.
ProtoShares (and a few other coins, I believe) focus as much on being memory-hard as CPU-hard. While CPU/GPU can be "cheated" by designing ASICs, there's no such thing as application-specific memory, making it a better candidate for an honest signal. [1]
Won't that just lead to people making machines with giant racks of RAM, causing the exact same difficulty race as we're seeing with the giant racks of ASCIs in Bitcoin?
And even if that's not the optimization (I'm not an expert on ProtoShares or memory-constrained algorithms), I am highly skeptical of anyone claiming a computation problem is optimally solved by a laptop, and cannot be optimized with custom engineering.
It's about cost versus yield. Custom-designed ASIC chipsets are orders of magnitude more efficient at their intended task compared to general-purpose CPUs; whereas it's impossible to buy or make "special" RAM, and cheap RAM is something everybody wants for everything anyway.
That may be true, but there isn't any convincing evidence that botnets are targeting (for example Primecoin and Protoshares), at least I am not aware of any, and I follow this area fairly closely.
CPU-only mining would be a lot more decentralized, if such a thing is even possible.