I did Darwin to Adelaide on Ghan Gold class (yet another perk of the job

) last February - Beautiful trip. It's amazing watching the landscape of Australia change from lush green to desert red in a matter of hours.
The whistle-stop tours are highly recommended if you have the cash to do them, especially the Katherine Gorge tour.
I was the youngest person on the trip by about 20 years but it didn't matter, you get to meet and speak to alot of really nice people from around the world, who's sole intention it was to see Australian wildlife in it's natural habitat. It so happened that the local fauna weren't too interested in coming out to play on our journey though, until the final morning when the breakfast carriage went into mayhem as two wallabies hopped away from the train track
The food is SUPERB. Their banana cheesecake is the single best thing I've EVER eaten in my life
Only negative of course is that you barely get any sleep, the beds aren't the most comfy and hard to doze off to the sound of click clack all night
As you come into Alice, the train slows down past some fenced indigenous communities which aren't exactly the best advertisment for traditional Australians. Cyclone fences littered with dirty nappies and beer bottles and cartons and deplapitated firbo huts which act as their homes.
Otherwise can't fault the trip. Don't know that I'd pay to do it though...