I guess that by "bundling" you refer to present several notifications of the same type as a single element.
I think that aggregating them by type is something really good for certain kind of notifications, but other content-related notifications may benefit from being aggregated by content.
Thats especially relevant when several individual events are correlated or can be interpreted as signs of a more global event (which is somewhat related to the concerns raised by Chris).
For example, if a page receives 1k reads, 20 comments and 2 cross-link, it may be useful to present that as a single "Your page on Higgs Boson is becoming popular (1k reads, 20 comments and linked by 2 other pages today)".
More than a specific solution I wanted to make sure that different kinds of aggregation critera are considered when the "bundling" discussion happens.
Pau