Special dividends are usually reserved for cases of extraordinary items generating surplus cash.  Or in some cases similar to the UK model (interim and final dividend) the company pays out the quarterly amounts and then issues a "top up" at year end according to how well or bad the year was.

Like Rick I don't think share repurchases provide nearly the benefit to shareholders that higher dividend payments do.  Primarily because the value is so easily lost or distorted over time.  Yes in theory it can be seen when doing analysis on a per share basis - but in 30 years of investing I can't say I have ever been able to attribute a portion of my return to share buybacks in a meaningful way.  Where as the higher dividend provides both the cash flow and the yield measurement.