What Improvements Will 64-Bit Processors Bring?

RyanG asks: "Everyone always looks at numbers (MHz, RAM, HD) when they're considering buying a new computer. Recently, more users have been eyeing bits, as in 64-bit processors, namely the Itanium and to a lesser extent the G5. A lot of people remember the performance increases that were seen when moving from 16 to 32-bit processors and some people seem to think similar performance increases will be realized when moving from 32 to 64-bit pocessors. From what I've read this isn't going to be the case given that 64-bit percision isn't needed in all but a few cases and that moving around that extra data can actually hurt the performance of 64-bit processors when compared to 32-bit processors. Anyone care to comment?"