Loading the hyperref
package and using
url = {http://www.usenix.org/events/osdi04/tech/dean.html},
gives a clickable url
in your bibliography.

alternatively you can use
note = {\href{http://www.usenix.org/events/osdi04/tech/dean.html}{my text for the link which can break across lines}},
which gives a link which has different text from the link. I agree with @Mico- this is probably a bad idea in general for a variety of different reasons.

Complete MWE
% arara: pdflatex
% arara: bibtex
% arara: pdflatex
% arara: pdflatex
\begin{filecontents}{mybib.bib}
@inproceedings{dblp,
author = {Jeffrey Dean and
Sanjay Ghemawat},
title = {MapReduce: Simplified Data Processing on Large Clusters},
booktitle = {OSDI},
year = {2004},
note = {\href{http://www.usenix.org/events/osdi04/tech/dean.html}{my text for the link which can break across lines}},
bibsource = {DBLP, http://dblp.uni-trier.de}
}
\end{filecontents}
\documentclass{article}
\usepackage[backend=bibtex]{biblatex} % bibliography
\usepackage{hyperref}
% bibliography
\bibliography{mybib}
\begin{document}
hello world \cite{dblp}
\printbibliography
\end{document}