I've learned the following:

The portable version omits the sample files and the Mozilla Firefox and Thunderbird extensions.
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"The portable version does store most of its settings in .ini and .dat
files in the same path as th EXE (only if it is actually installed and run
from a removable drive) rather than the registry/file system. But you can use the non-USB version and still backup your settings as well:

http://www.kinook.com/Forum/showthread.php?threadid=2935 "
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-c