I have a tomato garden and I usually roto till before the season around end of may and at the end of the season around October. I herd that you can over till the soil? Is this correct? Could that have any effect on the crop production? The last few years the tomato's have been so so. Any tips would be great.

Are you adding anything to the soil when you till? I've never heard of "overtilling" but I do know that tomatoes are very demanding on the soil and if you don't replenish the soil nutrients, your yield and quality will suffer.
If you've already planted, get some good water soluable fertiliser at your local garden center, one specifically formulated for veggies and tomatoes.

Add compost in spring, and if your soil is dense or very heavy on clay componants, you might want to add peat moss to aid drainage, promote root growth and prevent root mildew and decay.

Till in high nitrogen amendment in the fall so that they have time to "cool" before you plant- Horse manure,chicken and bat guano are popular.

I don't think you can over-till, but you can over-use. If you are using the same patch of land again and again you are depleting the nutrients in the soil. You should rotate your crops, grow something else there (in a different family) and then grow tomatoes again in a few years.

Read this.

Very interesting cons to tilling.

I've added peat moss, manure, and lime into the soil in the past before planting and tilling that in but in the past few years, I haven't added much of anything just stuff into the holes I dig for the plants. Next spring, I might do a soil test to see if any thing has been depleted since the last test I did in 2005.

If you can, you should think about rotating your plants.