There is a great article in the September/October 2009 edition of the ABC Organic Gardener magazine on tomatoes. It is written by the knowledgeable and sprightly Peter Cundall. The entire article is a fantastic read, but the part the I found the most interesting involved torture.
Funny enough, I did this exact thing about a month ago. I was given some tomato plants in small cylindrical pots (shaped like a glass which is taller than wide). I left them in the pots for at least a month after they were given to me since I did not have a place to plant them yet. So there they stayed getting watered with the rest of the potted plants. They were not given any food, so they quickly used up what little nutrients there were in the pot. Yet they started to flower and even fruit (that's how long I left them). When I did finally plant them out, I used the tried and true trick of planting them deeply by removing some of the lower growth and planting just below the remaining stems.
In the OG article, Peter recommends giving the tomato plants some potassium when they are potted on from the one week seedling stage. He also indicates that the plants can be transplanted into the garden once they have started flowering. As once they start flowering, they will no longer waste their energy producing leaves and focus more on delivering what we are after, the fruit.
Now in the very same garden bed where I planted the tortured tomatoes (see left-hand side photo), I also planted some of my own mollycoddled tomatoes (see the green mass in the background of the right-hand side photo) which did not experience the pain of being root bound. Well guess what? All the ones who had it tough in the pot are producing fruit, without exception. However the ones that I grew are looking very nice and leafy, but have only recently started flowering. Thus they are still a long way off from providing me with food. Basically they are being slack as I gave them such a cushy start in life.
So there you go, it is worth bringing out the thumb screws on plants such as tomatoes.