[schoen]

Not using primes anywhere near the range of the largest-known ones.

The primes in your RSA keys are likely to be 1024-bit primes, or about 308 digits.

[hansvm]

Plus, the (known) large ones are all of a nice enough pattern that you could almost factor just by looking at the digit count of the product.

[schoen]

Or by finding them in one of the lists of largest known primes. :-)

[hansvm]

Yes, sorry, the implicit assumption I accidentally left in my head is that when we're talking about factoring being important, it's products of 2 biggish primes (hence an answer one step removed from the lists of largest known primes).