I have used Gitzo tripods since I became a pro and still have my original heavy metal tripod that I lugged around the world. As the much lighter carbon fibre tripods became readily available I swapped to the 1548 which has done stalwart service ever since. Just before Focus this year I was shown a brand new carbon fibre tripod, the GT3540LS, and this has now become my tripod of choice. The new edition of the Gitzo 6X tripods are lighter, tougher and have the revolutionary G-Lock system to control the legs. Getting a tripod extended (or usually for me un-extended in a hurry with frozen gloved hands) is always a teeth gritting experience, well not anymore. The new G-Lock system means that a simple light twist immediately unlocks the section, which makes the whole process much more foolproof.
The GT3540LS is a four section tripod that is supplied with a centre column, perfect for long lens work close to the ground. I use it with my 500mm lens and it is great as it is a fraction of the weight of my old 1548. This was noticeable last week when I was hiking up a Scottish hillside with it, and also noticeable on the two foreign trips that it has so far accompanied me on. In these days of excess baggage charges it is nice to have a tripod that can be packed without worry. You can see the tripod here supporting a 300mm f2.8L lens whilst I was photographing Red Squirrels last week.
Perhaps an interesting point to note as well is the green element of Gitzo and their tripods; the company has many green practices and the tripods come in a recyclable bag without any plastic (other manufacturers please note). Worthy of a mention that I think.
So in short the Gitzo GT3540LS is a great, versatile tripod that I will be using from now on for all of my work and I hope that perhaps you will consider doing so too!