You should be aware there is a schedule change coming into effect on Monday, April 7, 2008. A quick glance at the schedule the other day didn't seem to find any real changes. I picked up a hard copy of the new schedule and compared it line-by-line with the April 2007 schedule.
Inbound to Boston
From Forge Park, 2 trains start sooner (#790, #720), 2 start later (#718, #796).
From Norwood Central, 2 trains start sooner (#792, #794)
From Walpole train #738 starts later.
all other trains start are scheduled to star at the same time as the prior schedule.
Now it would make sense that if the train starts earlier, it would arrive earlier but that is not always the case. It is true for the two trains starting from Forge Park and the one from Walpole, but for the two starting from Norwood Central, they arrive later as they travel the Dorchester Branch (bridge construction for next couple of years). There are also two trains that while they remain starting at the same time, they are currently scheduled to arrive later (#710, #798).
Outbound from Boston
Four trains are scheduled to start earlier (#705, #795, #713, #737).
Starting home early doesn't give all of these trains an advantage, the #795 actually completes later (via the Dorchester Branch) while the other three are scheduled to arrive earlier.
Five trains all leave South Station at the same time but are scheduled to complete their journey later (#735, #799, #719, #721, #729).
One of these (#799) goes via the Dorchester Branch and yet the schedule adjustment does not take into account the 10-15 delay recently experienced due to the bridge construction. Maybe, with other changes in schedule for other lines the 799 can run closer to its schedule. We'll see.
Schedules are available at South Station and online here.