Gingerbread is not designed to utilize 2 cores. Some apps can be specially coded to do so. From personal experience, going from a DX to a DX2 (both on GB) was very minor (except for the crappy pentile display on the DX2)
No. Gingerbread is not designed for multiple cores.
Actually, Gingerbread does support dual cores, there are just no apps yet that are optimized for dual core(or maybe just a few but I am not aware of any)