Indeed if one was observing the entire network, they might be able to piece together useful metadata as you both suggest. The kind of thing you might do with a NarusInsight. Tox and Zerocoin have done some interesting work towards this end and it's definitely something for us to consider going forward.

Thank you lawl & 18pfsmt for highlighting protection of metadata vs. content. At this time protecting content seems like the minimum bar by which one should measure, with metadata protection being the ultimate goal without sacrificing performance or convenience.