I don't know what species they are but given the location I suspect they're mostly harmless. There really isn't a great deal of anything of non-African origin that is dangerous to man here in MetroParkCentralis. On the other hand, having a tiny spider drop down in front of one's eyes while washing up after dinner or while sitting in the office composing another brilliant blog post can be somewhat disconcerting.
We're talking spiders. They descend on a single thread from on high. In the warm seasons I run across them as I walk down the sidewalks in my neighborhood as the wee spiders descend towards the earth. I think they were born in the tree tops. The same wee spiders also tend to drop down from the ceilings in my house.
I don't know what they are and they're pretty small and this isn't Australia or Alabama so they're almost certainly harmless. OTOH, I'm not all that comfortable with spiders dropping into my soup or onto my head.
I never experienced this weird phenomena when I lived anywhere else. Oh sure I had 22,003 tiny baby spiders crawl out of the earpiece of a special phone I hid under my sofa back when I was living in Emeryville but they were fairly easy to get rid of in short order. These guys just appear randomly and drift into my sight from time to time with no apparent cause or origin other than somewhere above me.