The performance advantage of 64-bit over 32-bit Ubuntu is clear. If you are still running the 32-bit version on 64-bit capable hardware you should really consider switching with the "Precise Pangolin" now that the 64-bit Flash is on par with the 32-bit version, OpenJDK works well on 64-bit, etc. The 32-bit situation should at least become a bit more interesting with Linux x32 support.
Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.