Primecoin searches a much more big primes, now minimal length is 320 bit.. it not so easy.
79910197721667870187016101
3713806433365297179049547921059040093141987810270452924175027055917982614990738 71883343191967359
First number from wikipedia 19ch, second is found 15ch from block 2592901.
In addition to being much bigger, the primes mined by primecoin have special limitation (the base prime origin must be divisible by block header hash) instead of any random number. I believe this makes the mining more complex and harder to find longer chains.