TERMINALMAN  Note that this is advertised as "officially supporting" Intel-based laptops only. The iMac seems not yet officially supported, which could account for your difficulties.

There were a number of different Intel iMac versions released (three as of May 2009, I believe) and Apple likely changed the fan control interface with each version just as they seem to have done with the new laptop versions.

It is likely that the author does not have access to all of the Intel iMac variations, so complaining IN CAPS that it does not work for you is a bit over the top IMO. Particularly for freeware/donationware.

This is a useful app, works perfectly on three (different) Intel Mac laptops in my family, and will hopefully soon support all the different "respins" of the Intel iMac.

Honestly, software is not so trivial to write when the interfaces you're using "evolves" over time. Been there, done that, got the grey hair to prove it.  
(Version 2.2.2)

TERMINALMAN  I have not had any problems using senuti, but I did read their Senuti Help pages several times first (start Senuti, then select the help menu->Senuti Help). Do this *before* you connect up your iPod.

Basically you have to make sure that the iPod is set to not automatically update from iTunes as soon as it's plugged it.

It's clear that if you don't do things in the right order in some cases then iTunes might wipe all the music from your iPod, which is what you're trying to avoid...

So follow their instructions carefully. Especially if iTunes pops up and asks if you want to wipe out the iPod contents with what's in iTunes, SAY NO!!

I used senuti 0.33 to transfer 3500 songs from iPod into my new Macbook, so far everything seems good and all the music I wanted transferred is there and sounds just like before.  
(Version 0.33)