It doesn't really even affect 1024 bit keys as even the largest RSA keys factored (this one is close but isn't) are quite a bit far away from 1024 (remember factoring difficulty scales exponentially with number of bits, not linearly). But 2048 bit keys are recommended I believe.
I don't think it's that simple. A 4096 bit key is extremely unlikely to get you fewer bits of security than a 2048 bit key. But the thing that makes 2048 bit keys a realistic threat is likely to make the "preference" be for something other than RSA entirely.
I know some of the CAs are using 4096-bit keys for their long term signing keys, but those are going to be in use for over a decade and are a major target. Everyone else seems to use 2048-bit.
I know that being able to factor ~670/1024-bits isn't that impressive (overall). But the fact that it is possible to develop the software this far shows that it's mainly a hardware problem. Enough parallelization into GPU cores with a significant system, and I think that cracking a 1024-bit key comes to less than a week.
