Forum OpenACS Q&A: Response to Email alerts grouped by topic
The best solution that I see, given the capabilities of ACS, is to allow people to choose their own formatting. There would be a default format, but users would have the ability to customize it for their alerts. It doesn't even need to be all that complex - just some toggle buttons like "I want the forum name in the subject line - yes, no".
I just entered this as a feature request into SDM. http://www.arsdigita.com/sdm/one-ticket?ticket%5fid=11861
p.s. In the near future, I ask that the OpenACS bboards add the poster's name and email address to the mail like you get on the aD bboards. Without that, you have no idea who posted the message without visiting the thread.