With Apple's latest update to Safari (version 6), they have combined the URL bar and the search bar into a single text field. This means you type your Google searches in the same place as you type your URLs. An unfortunate side effect of this is when you try and go to a website that Safari doesn't recognize (like one of your virtual hosts) Safari will search Google for that phrase rather than going to the URL you entered. For example, entering "mywebsite.dev" will search Google for "mywebsite.dev" instead of going to "http://mywebsite.dev".
To fix this problem, always enter your virtual host with the FULL URL. That includes the http:// part. Using the full URL will force Safari to go to that website instead of searching for it.