Are the spiders in my backyard dangerous?

Every year in late August here in Berkeley, CA, spider season arrives. This particular variety are speckled brown. They start out small (I assume those are the young ones), but in a month or so will turn into gigantic, fat, scary things as big around as a silver dollar and with abdomens an inch thick. In my small backyard right now are probably 10–12 webs, with more showing up every day. It makes gardening rather unpleasant because I constantly have to check to make sure I’m not going to stick my hand (or my face) into a gigantic spider web, not to mention the spider itself. I don’t think I’ll ever escape the squiggly feeling the spiders give me, but it would be nice to know if they are actually dangerous so I could garden with more peace of mind.