Lower power consumption, due to the the smaller die size. Less heat output due to lower power consumption. More overclocking headroom than their 65nm counterparts. New SSE instruction set with the Penryn models. High k hafnium gate architecture is able to switch faster than previous 65nm counterparts.
SSE4 which will increase media performance a lot.
About 15% faster at everthing per clock.
Basically a little better in every way and cooler like mathos said.
A major redesign will happen in about a year with the Nehalem.
SSE4 to be more precise. Only beneficial if you do video encoding using a codec that is optimized for SSE4 instructions. DivX 6.7 or 6.8 has an experimental SSE4 mode, and I think encoding performance boost is about 30% over not using SSE4.
High k hafnium gate architecture is able to switch faster than previous 65nm counterparts.
In other words compared to a similarly clocked (CPU speed) Conroe, the Penryn has been tested to perform about 0% - 10% better depending on the application. I think gaming was on average 5% or 6% improvement. The highest was with video encoding for about 10%.
Part of that increased performance can also be attributed to the larger cache.
Added Level 2 Cache is also a bonus in performance for some applications. Higher range duals go from 4MB to 6MB, low range duals go from 2MB to 3MB, low range quads will have 2x3MB and higher end quads will have 2x6MB.