Well, the Mrs and I only did it for six months, but it was bloody brilliant. And we could have quite happily continued indefinitely. It's strange because it is a very simple life, i.e. you get up, you cycle, you camp; but at the same time it is incredibly full. You have more fun, more adventure, experience more pain and meet more humanity in one day on the road than a week back home.
We cycled through some very bad weather, but we never contemplated giving up. In terms of adverse weather, very cold and dry is no problem - you just wear more layers and have a good sleeping bag. Cold and wet is a bit more problematic as you have to spend money on B&Bs to dry your kit out. As long as you have good waterpoofs not much can defeat you.
In general it is easier being a perpetual nomad in poorer countries, where accommodation is cheaper and people are more hospitable.
If we ever have the opportunity to go away for a year, we'll be off like a shot.