In response to a question on SABR-L I dug into retrosheet data for 1992 (I now have the 2003 data but haven't loaded it yet courtesy of the Stats Software group on Yahoo). The questioner asked how often triples drove in runs, how often the batter hitting the triple scored, and how often both occurred. Here's what I came up with:
Lg 3b RBI Score3b Pct 3bScored Pct 3bRbiScore Pct
NL 459 289 207 45.1% 316 68.8% 117 25.5%
AL 386 264 187 48.4% 252 65.3% 93 24.1%
Where Score3b is the number of times a triple drove in at least one run, 3bScored is the number of times the batter who hit the triple scored, and 3bRbiScore is the number of times the batter drove in a run and later scored in the inning.
If I did the calculation correctly (this was my first effort at doing inter-inning analysis with retrosheet data) it is suprising that 46% of triples ended up scoring a run or more since the OBP is roughly .330. That means that triples are hit more frequently with men on base than you would expect. The percentage of batters hitting triples that score seems about right (67%) when looking at run expectancy tables.