it's a dual core, but each core performs a lot better than a 2006 CPU, also HT makes this CPU handle 4 threads a lot better than 2006 dual core CPUs, at the best cases it performs much higher than a 2006 CPU and the FX 6100, now on the worst cases (MT, rendering like:
http://www.hardware.fr/articles/863-13/rendu-3d-mental-ray-v-ray.html) we are talking about +- q6600-q6700 stock performance (but with much lower power usage), so for ST the i3 is MUCH faster than a 2006 CPU, for MT is equivalent to a quad core from 2006-2007, now the i3 supports instructions that the 2006 CPUs doesn't and it have much higher I/O performance I think, so it's not accurate to compare it to old dual core CPUs.... now for gaming and basic usage the i3 is great, for rendring not so much, but still much better than old dual cores.
in some cases it's clear that the i3 lacks in terms of MT performance, but single/dual core performance is still important for many applications, and the i3 is clearly faster for that than the FX6100, so it's not that simple.