The tutorial by Peter Wegner.
A very interesting, thought-provocative presentation, which was unfortunately slightly watered-down by a lack of focus: Wegner couldn't resist reviewing the whole world (Java, Corba, etc.), without the deep insight driving his main topic.
His starting point is the claim that Turing machines are not powerful enough to model complex distributed systems. The reason is the assumption upon which they are built, that they may process their input by finite chunks, one at a time. Wegner proposes an extension with interaction machines, which get stream input which may affect the processing itself.
Objects may have non-algorithmic behaviour.
Wegner made very strong point against formalization, and opposed it to the non-algorithmic expressiveness of interaction machines. For example he argued that off-line planing is algorithimic, but combinatorially explosive, whereas on-line planing is non-algorithmic but efficient.