For those curious about the performance advantages of using 64-bit Ubuntu Linux over 32-bit Ubuntu on a modern Intel laptop, here are 32-bit vs. 64-bit benchmarks of Ubuntu 14.04 LTS on the ASUS Zenbook Prime.
Going back years we have run 32-bit vs. 64-bit Linux benchmarks. While the results seldom change, we keep running them as the question of choosing between a 32-bit and 64-bit Linux distribution image is still a popular question... These tests drive in a surprising amount of traffic and I continue to be flabbergasted by the number of people still asking this question when nearly all modern x86 Intel/AMD hardware fully supports x86_64 and it generally means much better performance. Usually the only caveat in not using a 64-bit Linux image is if running a system with less than 2GB of RAM.
In the past there were issues surrounding the Java and Flash support for 64-bit Linux along with an assortment of other possible problems (e.g. with Wine), but all those major issues are a matter of the past. 64-bit Linux is in great shape and as long as you have a decent amount of RAM you really should be running 64-bit Linux. There is also the Linux x32 ABI that tries to bring some of the x86_64 CPU advantages while using only 32-bit pointers, but Linux X32 hasn't gained much adoption.
Using the recently released Ubuntu 14.04 LTS I ran benchmarks of the 32-bit (i686) and 64-bit (x86_64) Trusty Tahr releases on the ASUS Zenbook Prime with Intel Core i7 3517U (Ivy Bridge) processor with HD Graphics 4000, 4GB of RAM, and dual 128GB SanDisk SSDs. Ubuntu 14.04 LTS was left in its stock configuration during all of the open-source benchmarks that were driven via the Phoronix Test Suite.