Primecoin? It's not solving a "problem" as it claims, there's nothing that can be solved with chains of primes. They're interesting but that's about the end of it. The vastly smaller network means it's a lot more susceptible to attacks.
It's not different from SHA-256 or scrypt in that regard. However there appears to be some interest in these primechains from the scientific community. I never claimed it is solving important "problems" but I like the CPU only property. The Bitcoin GPU/ASIC race favored a few wealthy individuals. 40% of all BTC is in the hands of a few people. I don't see this happen with Primecoin at the moment. GHash.io looks more like a problem for Bitcoin as e.g. botnets for Primecoin.
I'm more interested in better and faster miners for Primecoin as this is a pretty interesting problem to solve. Getting rich with either of these coins is pretty much impossible if you are not already wealthy and able to invest a good amount of money and energy - especially in the BTC ecosystem.
