Michael Coleman posted some of the benefits of the new 64bit Adobe After Effects CS5, that its faster.

“First of all, After Effects launches more quickly — more than twice as fast.
Dealing with files is faster. Reading and writing certain compressed file formats is twice as fast. We have also parallelized QuickTime export. This improves the performance of common tasks like transcoding files into other formats.
Rendering is faster. In the simple cases, when rendering on a single core, we are seeing 20-40% shorter render times. This is a result of general efficiencies gained during the 64-bit conversion. As a result, each core on your system is being used more efficiently and you can expect to see greater utilization for each CPU core.
Of course, virtually everyone has multi-core CPUs nowadays. Have you ever used the “Render Multiple Frames Simultaneously” option in the preferences? There are several key improvements in this area as well. We have completely rewritten the After Effects multi-core processing engine for CS5. Benchmark projects are rendering with 30-50% shorter render times. That’s up to twice as fast!
In CS4, there was a significant lag when starting up multi-core processing (MP). For short renders, it was often faster to use fewer cores. This is no longer the case in CS5. Starting an MP render may have taken 30 seconds in CS4, but it is 1-2 seconds in CS5. If you’ve been avoiding using MP for RAM previews for this reason, this one is for you.”