While most x86 hardware shipping in the past few years has been x86_64-capable, Canonical has continued recommending the 32-bit version of Ubuntu Linux over the 64-bit version. With Ubuntu 12.04 LTS "Precise Pangolin" this will hopefully change where the 64-bit version becomes recommended as the default spin. In this article are some updated benchmarks showing the performance of the 32-bit versus 64-bit versions of Ubuntu 12.04 LTS.
Most cases for using the 32-bit version over 64-bit Ubuntu are now no longer relevant. When it comes to Intel/AMD hardware, nearly all of the hardware shipping in the past few years is 64-bit capable. Additionally, earlier 64-bit Linux issues like Adobe Flash player problems, Wine issues, or 64-bit Java support have since been addressed. There really is no longer any big reason to stick to the 32-bit version of Ubuntu when the hardware supports 64-bit. The 64-bit edition of Ubuntu is faster, hits less peculiar bugs, and nearly all-around is just better.