In general I would say yes. Search engines want to return the best results so the most usable sites are a part of that. Let's run through some of the main on-site optimizations:
Page titles in <title> tag:
The page title is shown in several places: the browser's window title bar and/or tab, bookmarks (as default name), search results and often in other links pointing to your site.
Headings in <h1> tags:
Headings provide a clear structure to the page and makes it clear what the page is about.
Simple, static-looking URLs:
This makes it much clearer, when seeing links from other sites, what the target page is about.
URL stability:
In other words, every piece of content has one canonical URL. If /hello.html and /goodbye.html contain the exact same content, that's pretty confusing.
Keyword density:
This is an area that gets way too much focus but if you look at the extremes it's obvious that a page loaded with the same word or phrase over and over is not good for usability and readability.
Site speed:
A fairly minor factor which probably gets more attention than it deserves. Regardless, faster sites are clearly more beneficial to users.
However, it's not all good: there are some optimizations that may harm usability. The one that springs to mind is keywords towards the start of the page title. See this Pro Webmasters question. This may encourage site owners to spam keywords at the start of a title, making it less clear what site you are going to. Even Stack Exchange does this, taking up valuable space on the browser tab and making it harder to find the desired page amongst several tabs.
