Adel Gadllah (dragoo1) ran my script on his computer with a couple other compressors: pbzip2 (a parallel implementation of bzip2) and pigz (a parallel version of gzip). His computer is a quad core with 6GB of RAM. A definite upgrade from the machine I tested on (dual core with 1GB of RAM). The results are quite interesting.
Since no new algorithms were introduced, just new implementations, the compression ratios didn't change much. But the times for the parallel implementations were very interesting. pbzip2 runs faster than gzip. pigz -9 runs faster than lzop -1! If compression was the only process being run on the machine then the parallel implementations are definitely worthwhile.