Alll the ones I have seen have been 50 cent coin large.
We used to find them in the garage fairly often.
The closest I ever came to a bite was cleaning my dads back yard out, he had tons of GTO body parts just stored outside piled on top of each other. (you can do that in cali and not worry about rust to much) So I grabbed a radiator brace that was messed up from a front end accident, and flipped it, 3 freaking inches from my fingers was a huge one!! I screamed like a women and tossed the brace, these things are as wide as the front of the car. It landed spider up and the bastage had not even moved!!!
Brake cleaner took care of it.
I started wear heavy leather work gloves after that.
I second the brown recluse thing though, they are not web spiders, they wonder so you have more of a chance to get bit. The widows, as long as you do not go sticking your hands in dark places without looking you are ok!