I came to the conclusion that there was no point investing in a tripod if you didn't have it with you when you needed it. So I looked for the lightest, smallest tripod I could get that could handle the heaviest weight I would ever likely have. Thom Hogan has some good articles about this - bythom.com
. Basically, he says go for what you need straight away, and save yourself a ton of money in not having to throw out cheaper tripods...
For me, the answer was the Gitzo 1541T. http://www.gitzo.com/series-1-6x-4-section-traveler-tripod-with-g-lock
This thing is tiny. It fits into a rucksack with ease, and weighs almost nothing. Yet the rated load weight for the thing is an incredible 8kg, and it is amazingly stable when it's up, especially if you keep the centre column down.
I'm sure some will quibble about lighter-weight tripods, and I guess if you have heavy, long lenses, this might be an issue, but it depends how willing you are to lug a really hefty tripod. Like I said, the best tripod in the world is no use if you decide you cannot afford to carry it where you are going. I carried this Gitzo all over Yosemite last year, and never noticed the weight. You can hang a bag under it to give additional stability - there is a pull out hook thingy.
The downside? It costs an absolute fortune. There is always a downside. And it struggles a bit with my Mamiya RZ67, but then that's a bit unfair, right?