When I bring up the meta.stackoverflow.com home page, links I've visited are highlighted with #666666 and the others are highlighted with #3d3d3d. This is hard on my eyes! It's hard to notice the difference. Maybe #666666 could be changed to #999999 or maybe a hint of green? (#9999bb)
I'm guessing I should tag this as a bug... feel free to retag if this is wrong.