eh, fair point, that it depends on your preference.
If that's what you want to do, I need to make a change to your suggestion, though: The partition you want to make HFS+ (and then extend) needs to be the first partition of the drive - the commandline tool that extends partitions can only go towards the end of the drive (kinda like Vista's partition extender), and iPartition
is kinda expensive for this one-time use. But it does seem to work; I used it once a long time back (when 10.3 was the current OS) and it managed to not completely destroy my data (though I did have that data burned to DVD just in case).
edit: one other good reason to re-partition in OSX is that you can use the GUID partition map. That allows you to install OS X to an external drive, should you choose, and boot from it. A real OS X DVD won't install to a drive (even with an HFS+ partition) unless it's GUID on an Intel Mac (or Apple Partition Map drives on a PPC Mac - however an Intel Mac will still boot APM partitions, so if you want a universally-bootable drive, partition it and install OS X on a PPC Mac, and you could move that universal bootable drive to any Mac).