I thought the mattmattson reference was useful and instructive, but the other two are irrelevant to the question - neither says anything at all about transactions, and that's the topic of the question.

However, it's a nice question. It's not at all surprising (and therefor not particularly interesting) that the two task types which can't support transactions properly are one that deals with file storage not database storage and one that deals with XML not atomic values, so both pretty distant from relational theory and practise, but it is something that anyone who wants to use SSIS (whih certainly doesn't include me) needs to know.