I've been reviewing my company's analytics recently, and a lot of people are using search engines to search for the company URL, or URLs within the company. It probably equates to less than 1% of search terms, but it's still more than I would expect, particularly as it slows down access to sites. Arguably browsers that allow searching from the address bar have blurred the boundaries between searching for content and going there directly, but I'd like to know if anyone has done any research into why people do this.
Many people have only a fuzzy awareness of the distinction between "The Web" and Google / Yahoo / whatever their homepage is set to. Therefore, such people often use the Google search box (or whatever) to enter URLs rather than the browser address bar.
Google may have noticed this behaviour when developing the combined URL/search box in Chrome.
Consider what happens if they enter it incorrectly.
Address bar: nasty error message, have to try again
Search engine: "Did you mean..." and often a single click to get what they want
I have observed this on a number of occasions and I believe people are confused because:
a) They use a search engine as their default homepage
b) A search box is visually similar to an address bar
c) Google (and others) auto-focus on their search box when visited
More importantly, less computer-savvy people look down at their keyboards when typing, especially for long URLs, and miss out on the fact that they are actually typing it into a search box.
Furthermore, since modern browsers use combined address bars and search boxes, this makes the distinction hard.
I think this depends on whether these are new or returning users. You may be able to see a correlation between the % of new users a month with the % of users who arrive from search.
Your analytics should also provide the graph of web browsers which could lay further credit to the other answers around user behaviour with omnibox.
You may find that there are a combination of reasons why users would rather search than type in the url.
Personally, I use sites which are following the current trend of not spelling their names correctly e.g. tumblr, toggl, dribbble so I've learnt to let Google handle the telling me where I want to go