Also, don't plant cherry tomatoes next to your regular tomatoes. Generally, tomatoes tend to pollinate themselves, but the structure of cherry tomato blooms makes them "promiscuous" (as Dr. Carolyln puts it).
When a hybrid variety crosses with itself, there's no telling what you'll get (it'll still be a tomato of course, but color, shape, size, taste might be like the parent or could be totally different).
OP (open pollinated) varieties are stable. Seeds from a self-pollinated OP plant will produce a plant of the same variety. Of course, a rogue is possible, but unlikely.
There have been successful efforts to de-hybridize some popular varieties. I think the effort with 'Sungold' cherry tomatoes is still a work in progress. Shoe (Horseshoe) says the OP Sungold has tougher skin and isn't quite as sweet, so he sticks with buying the hybrid seed.
For our newcomers, you can see we get really chatty and off-topic at times. Often, there will be a "chat" thread that's separate from the organizational thread for a swap. For a seed swap, I didn't think that was needed, as the only organization info I need from this thread is who is coming. :-)
Speaking of which -- IF YOU ARE COMING and don't see your name on the list in the top post, please speak up!