With the number of CPU cores in desktop machines moving from two to four and soon eight, the ability to execute computationally expensive tasks in parallel is becoming more important. The mgzip tools that can take advantage of multiple CPU cores during file compression, while pbzip2 uses multiple cores for both compression and decompression.
A file compressed with pbzip2 can be decompressed with the standard bzip2 program, while one compressed with mgzip can be decompressed with the standard gunzip utility. You can find pbzip2 packages for Fedora 8 in the standard repositories and install it using
yum install pbzip2. However, mgzip doesn't appear to be packaged for many distributions, so you must install it from source.