Everyone knows you can't save seeds from hybrid varieties. It is practically the first thing you learn as about seed saving. Too bad it isn't true. Not only can you save seeds from a hybrid tomato and many other vegetables and flowers, the result will usually be something you'll like better than the hybrid you started with.
F1 hybrid varieties were first created because they have hybrid vigor, which is just another way of saying that they aren't inbred. Inbreeding, as we all know, isn't a good thing, generally resulting in unhealthy individuals. That's why we don't marry out sisters and why purebred dogs don't live as long as mutts. F1 hybrid varieties are a way to bring the health of mutts to a uniform variety. (How that works).
In the plant world, however, things are a little different. Some plants, like corn, are called outcrossers and act like us and dogs. Their flowers are set up in a way to maximize the chance that they get pollinated by another, hopefully unrelated, plant. These types of plants show very strong inbreeding depression, so hybrid varieties are significantly more vigorous than an inbred equivalent. Other plants, including tomatoes, peppers, beans, and lettuce, are selfers. Rather than working hard to get the wind or bees to carry their pollen to another flower, they just self pollinate, naturally inbreeding in the most extreme way possible. As a result, their genomes have adapted to tolerate inbreeding, meaning hybrids varieties don't show significant increase in vigor.
Why then, hybrid tomato varieties? Why do seed companies go to all the effort of hybrid seeds when a inbred variety would work just as well? Simply put, because you “can't save seeds from them.” Introducing hybrids is a way for plant breeding companies to protect their varieties from other companies taking what they've created. Since 'Early Girl' is a hybrid, the only way to produce more 'Early Girl' seeds is to have access to the two parent plants used to create it, parent plants that you can bet Burpee is very careful no one else is ever going to get ahold of.
When you save seeds from a hybrid variety like 'Early Girl', you'll get a range of different plants, none will be exactly the same as 'Early Girl' itself. Fruits will be a little bigger or smaller, sweeter or tarter, everything will differ to some degree. However, the traits you saw in the F1 parents plant will be essentially the C average for what you'll see in next generation. Despite the variability, it usually isn't hard to select out a plant that is very similar to the hybrid variety you liked so much.
It is even easier, though, to pick out a plant that you like better than the hybrid variety it came from. Professional breeders have create varieties based on what they think the average gardener and will grow over as wide a part of the country as possible. But you aren't an average gardener, and you only garden in one spot. Maybe you'd like something bigger for slicing on a sandwich or something smaller for eating out of hand, sweeter or more acidic, drought tolerant or the ability to grow through chilly wet weather. Grow out at least half a dozen seedlings from a hybrid variety, and you get the chance to customize it for your climate, your soil, and your tastebuds. Keep saving seeds from your favorite individuals, and after a few years, you'll have a new variety, one that will perform and taste better for you than the hybrid it came from. Give is a name, share it with your friends, pass it on to you children, and you've just created your own heirloom.
Go ahead. Save those seeds!