Illustrations are a great way to give a design personality. And it doesn't matter if your website is a portfolio, a service, or an event -- well thought out and designed illustrated elements look good in a project. From simple and minimal illustrated details, to full illustrated backgrounds, there are a lot of options.
Here are some examples of illustrated elements in web design.
Cole Townsend.
Gruvual
The Society Inc.
Simple as Milk.
Hatched