FUD Zilla reports system builders are unhappy with the overclocking capabilities of Intel's Ivy Bridge, as production parts can apparently only go as high as 4.4GHz:
Intel is apparently currently apologizing to its customers that were looking at various Ivy Bridge reviews and wanted parts that can go as high as 4.8GHz, that Intel currently cannot deliver. This means that reviewed ES parts might be cherry picked, golden samples, and the situation with retail parts might be much worse.
A lot of system builders are living off their water cooled and overclocked systems and take much pride in providing the best possible "out of the box" stable overclock. Intel's Ivy Bridge chips are having trouble with overclocking due to higher temperatures and they are simply not appealing to system builders. Ivy Bridge might have better graphics and advanced tri-gate 22nm manufacturing process, but it looks like all is not well in Ivy Bridge land. That same 3D/tri-gate 22nm manufacturing process is probably the one to blame for delay and at least takes a part in the Ivy Bridge disappointing overclock potential.