When you search for papers on PubMed, it usually gives the results in chronological order so many new but irrelevant papers are on the top. When you search papers on Google Scholar, it usually gives results ranked by citations, so will miss the newest exciting finding. Students in my lab recently made a very simple but useful tool Gnosis. It ranks all the PubMed hits by (Impact Factor of the journal + Year), so you get the newest and most important papers first.
Emphasis added, as if I need to. You see, relevant and important papers are indexed by the journal impact factor. Of course.