Last year I pushed the season by 2+ months. I turned individual Earthtainers into mini greenhouses using stretch-wrap, small $5 candle warmers and a removable lid. My goal was to have ripe tomatoes by our last frost date - June 3. I planted the first few containers on March 31 and a couple more in mid-April. There was daily work involved. Each sunny day I needed to remove the lid and turn off the candle warmers - then put on the lid at night. I harvested the first ripe tomato May 27 and by mid-June we were giving the extras to the neighbors. In all, they survived 29 nights below freezing (15 degrees one night) and 56 nights below 40. In a normal year, we usually get our first ripe tomatoes late July or early August - and are limited to only short season varieties.
There are a lot of variations of what I did that could be incorporated. I posted a thread about the experiment -
http://www.tomatoville.com/showthread.php?t=26514.
Several of the ideas I tried early did not work as I hoped, but the experiment eventually evolved to something that, in the right circumstances, can let you 1) enjoy eating early varieties well ahead of normal and/or 2) try some of the later season varieties you only read about but can never get to ripen.