Safari relegates search to a separate field to the right of the address bar -- rather than allowing URLs and search terms to be used in one omnibar like Chrome does (below). This means that every time that I want to search (which is a lot), I have to tab over to the search field.
It may sound trivial, but how many times do you fire up your browser specifically to search for something? I do it all the time and tabbing over (or remembering to tab over) to the Search field is inconvenient and time consuming.
Even more annoying is that when I mistakenly enter a search term into Safari's location bar and hit return I get a spammy "Domain Helper" page from Comcast that's riddled with affiliate links. (Many Comcast subscribers don't know that they can opt out of Domain Helper.)
That's where Olivier Poitrey's free Safari Omnibar comes in. Safari Omnibar is a free Safari SIMBL plugin that allows you to avoid the Safari two-step by merging its location and search fields together (below), just like the Chrome location bar does.
If you're a Safari jockey, Safari Omnibar is essential. It's one of the first things that I install on a new Mac.