I missed this post on clogging the bases and the follow-on discussion on The Book blog which is very interesting. For what it's worth here are the advancement totals for balls hit into the outfield for the year 2000 (yes I have more recent data but was too lazy to dig it out).
Total To2nd To3rd Scores Thrown Out
Runner on First, Batter Singles, No Runner on Second
5896 4012 (68%) 1759 (30%) 52 (1%) 45 (1%)
Runner on Second, Batter Singles, No Runner on Third
3585 927 (26%) 2523 (70%) 128 (4%)
Runner on First, Batter Doubles, No Runner on Second
1537 902 (59%) 574 (37%) 61 (4%)
Now these numbers don't necessarily bare directly on the topic of the post since it was about clogging the bases and in these cases we're looking only at opportunities where there was not a lead runner in play. When I get a chance I'll take a look at the difference between when a runner is on in front in these situations.