I've been building 64-bit software deployments this week at work. Actually, just today, but maybe another round, who knows. The machine I'm using is a brand new HP 8600 workstation with 2 quad-core Xeon procs and 16 GB of memory running Windows XP 64-bit SP2. How much faster is it at building a software deployment tree than my two-year old, 32-bit Dell Dimension E520, with a single core Pentium 4HT proc, and 4 GB of memory, running Windows 7 Ultimate (32-bit of course)? Zero difference in speed! None. No difference at all.
What is different with this "powerhouse" workstation is how many apps I can simultaneously before everything starts to bog down. Granted, most installers are not tuned for 64-bit execution, nor are they optimized for multiple, multi-core processors. And I also know that this is not the ideal basis for comparison, but I thought this was kind of interesting anyway.