Well, the topic title says it all.
I don´t know about you guys, but I hate to wait downloads, my solution to that is that I do it while I am sleeping (I am sleeping, so I don´t care anyway) and it sux that my computer still on after the downloads, NERO burning kit has this option, to turn off the computer after the burning.
I would love to see it on my limewire too, so I could do my downloads and wake up without the worry to turn off my computer.

It would be better to have that as a separate utility that shuts the computer down or hibernates it or whatever after a process, or a group of processes exit. That would make it a lot more generic and thus a lot more useful. It could also get a lot more developer's attention and be made to be a lot more robust.
It is likely such a tool already exists.