Recent high-resolution data of the exclusive proton knockout reaction (e,e′p) have provided evidence for the importance of nucleon-nucleon correlations in atomic nuclei. Thus similarity of nuclei with a correlated Fermi liquid rather than an uncorrelated Fermi gas of quasi-independent particles is indicated. We discuss empirical evidence in terms of the mass dependence and separation-energy systematics of spectroscopic strength deduced from the exclusive (e,e′p) reaction. A critical comparison with the findings of the proton pickup reaction (e.g. (d, 3He)) is then made. It is argued 0106 that spectroscopic results from the electromagnetic and hadron reaction may be reconciled by employing proper information on the radial extension of the bound state wavefunctions as deduced from the (e,e′p) spectral function data. Novel and more focused light on the issue of correlations is foreseen to be shed by data expected from the ≈ 1 GeV electron accelerators with 100% duty-factor that are under construction at present.