As answerers noted in my other question, time-of-day and day-of-week does affect your question's chances, independently of question quality. At the same time, there are probably bandwagon effects: popular questions become popular because they're popular.
<opinion>To maintain quality of SO ratings in the long-term, questions should be rated on quality (defined by the community, of course). The site should be structured to promote quality over luck.
How might SO be changed -- I'm talking about general ideas here, not the SQL queries that support them -- so that time-of-day/day-of-week effects be mitigated?