In this talk I will give a more refined quantitative understanding of some of the important known solitons in the n-dimensional mean curvature flow in R^{n+1}. The global estimates in question follow by iteration of monotonicity formulae - an idea and technique which, while quite elementary in nature, appears to be particularly useful in several of such situations. The applications of the explicit estimates are many. I will focus mostly on the new nonexistence theorems that follow. Time permitting, I will also mention other, related consequences for the analysis of the soliton PDEs for the flow.