I've been familiar with these tiny guys since childhood. Usually dusting or vacuuming corners send them scurrying about (and they're quite fast!). They're also found in dry nooks and cracks outdoors. I believe they are called wall spiders (oecobius), but I'd like confirmation and a species name (but my photo resolution likely isn't good enough for the latter).
Length is approximately 2mm.
Wall spider (family Oecobiidae). Harmless; appear to specialize on ants...
http://ednieuw.home.xs4all.nl/Spiders/Oecobiidae/Oecobius_annulipes_F3203.jpg
