The MBCR has a helpful sign posted in South Station showing the on-time percentage of its various lines. They don't say on the sign what "on time" means exactly, but anyway here are the numbers for the Worcester line, which is the one I use. They feel roughly congruous with my experience.
- 58.05% in November 2007
- 64.48% in December 2007
- 69.26% in January 2008
I might as well also point out that I'm currently waiting for the train, which is late.