What are your thoughts on epigraphs in theses? I am wondering if there is a general consensus as to the suitability of epigraphs in a thesis, either a single one at the start of the document, or an appropriate quote to begin every chapter.

For example, at the start of a technical chapter describing some code, I could write


  Beware of bugs in the above code; I have only proved it correct, not tried it. - Donald E. Knuth


I am lucky to have complete freedom over how I choose to typeset my thesis (Master's thesis in astronomy) and I like the idea of a thematic quote to begin a chapter. However, I am wary of seeming unprofessional or tacky so I am curious to get some more thoughts on the matter.
Well-chosen, non-frivolous epigraphs can enhance a thesis.