How much can users hold in their short term memory
This is a very simple question with no single answer, I'm afraid. The other classic paper quoted in this context is Miller's "The Magical Number Seven, Plus or Minus Two" (e.g. http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two). In the case of a user using a website, memory will also be affected by:


Familiarity with the subject. Is the website about a topic the user is intimately familiar with, or something completely new (unlikely) or somewhere in between?
Available contextual information. Can the user quickly get to supporting information? In which case, the load on memory may effectively be reduced
The extent to which the information presented on the site is related. The key message of Miller's paper is that people group ('chunk') information in order to reduce memory load


Not sure if your question relates to a specific problem, or if it's a general query, but things like memory limits are hard to define absolutely, hence testing should always take place in as realistic a context as possible.