Bad graphics drivers can cause extreme general slowness

For several months, one of my computers was being extremely slow for its specifications. There wasn't any clear bottleneck - things would stop responding for many moments even under very light CPU and disk I/O loads. I had intermittently tinkered with various settings and tried uninstalling things, but I only saw noteworthy gains after reinstalling the graphics driver (for completely unrelated reasons). Apparently the NVidia driver I had was poor. I'm not sure how it caused such bad general performance, but the new driver is much better.