An intriguing paper on the "Variability and memory of protein levels in human cells".
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17122776&query_hl=1&itool=pubmed_docsum

Might have important implications for 'phenotypic diversity/heterogeneity within populations of cells'.