The Grand Traverse starts on the shores of Lake Wakitipu and stretches the length of the Greenstone and Routeburn Valleys, crossing the main divide twice in the process. The Greenstone and Routeburn Tracks have long been New Zealand’s most accessible and popular routes into the spectacular South Island high country.
The Grand Traverse passes through two national parks: Fiordland and Mount Aspiring, and is part of Te Wahipounamu, South West New Zealand World Heritage Area. The pristine bush is home to a myriad of native birdlife: the Robin; Kea; Fantail; Parakeet; Bellbird; and Yellowhead, just to name a few. The sheer isolation and raw beauty of the Greenstone provide the perfect stage for the breathtaking scenery of the Routeburn. An unsurpassable combination to make a memorable walking experience. …
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Sure you could sign on with the tour (above). It costs between $1,600 and $2,500 New Zealand, depending on what optional extras one prefers. … Or you could do it independently like Scottwoz for about $100.
Here’s his independent trip report:
… Most of the scenery and landscape we covered was nothing short of spectacular and over the course of the five days we got to see a lot more than we should have, certainly more than the law of averages would normally allow. We hiked, on average, around six hours each day and covered an incredibly diverse terrain. …
In the Thick of it … The Grand Traverse, New Zealand – trip report
Sign me up.
I’m planning a return to New Zealand in 2011.
besthike.com 
My mum did the Milford track with Ultimate Hikes and really enjoyed it. She is 72 so it does seem acceptable to pay to only have a day pack, although I know people in their 70’s who carry full pack. Those who used the supplied rain jackets found that they leaked badly; for the money I think they could sort that out.
I am always amazed at the prices these treks can cost, while Peter Matthieson crossed South America on almost no money at all!
I did the Routeburn-Greenstone loop last summer independently. If you’re in reasonably good shape it’s no problem! Everything is well-marked and the huts are very comfy.
The guided walks are good for those who aren’t really backpackers, or can’t carry much. Otherwise, they’re a lot of extra money that you don’t need to spend. (Unless you’re unable to live without a hot shower for a few days.)