Interesting article in May issue of SFO magazine suggesting that there's an IV pattern on expiration day for stocks over $50 with large open interest. Barring major news, IV tends to increase until 11 AM, drops toward noon, levels off for 2+ hours and then drops sharply into the close. So if you're an expiration day trader, long positions may be best suited for the AM and short positions for the afternoon (straddles). It also suggests that ratio spreads may be a good vehicle as well. Obviously, one should not contemplate any of this unless one fully understands the ramifications of the strategy and has the experience and discipline to manage the risk.