There was some discussion [here](https://mathoverflow.net/questions/12511/what-is-yonedas-lemma-a-generalization-of) about special cases of Yoneda's lemma, including the usual examples of Cayley's theorem for groups and Dedekind's embedding theorem for posets.

It also seems that a good chunk of Tannaka duality can be seen as an application of the (enriched) Yoneda lemma -- see the [nLab page](http://ncatlab.org/nlab/show/Tannaka+duality) for discussion.