Is lensing of point sources a problem for future CMB experiments?
  Weak gravitational lensing from large-scale structure enhances and reduces the fluxes from extragalactic point sources with an rms amplitude of order 15%. In cosmic microwave background (CMB) experiments, sources exceeding some flux threshold are removed, which means that lensing will modulate the brightness map of the remaining unresolved sources. Since this mean brightness is of order 100 micro-Kelvin at 30 GHz for a reasonable flux cut, one might be concerned that this modulation could cause substantial problems for future CMB experiments. We present a detailed calculation of this effect and, fortunately, find that its power spectrum is always smaller than the normal point source power spectrum. Thus although this effect should be taken into account when analysing future high-precision CMB measurements, it will not substantially reduce the accuracy with which cosmological parameters can be measured. 
Max Tegmark, Jens Villumsen