What is the importance of consistency in the design of webpages?

Web design is about making the user feel comfortable on your page. It really should be called "web usability". Because the goal is to keep the user on the page as long as possible. For that they need to feel comfortable browsing your site.

Which means even though you can be creative, a good site design should follow some consistency and conventions. There are certain conventions they already are familiar with from browsing the large sites like Yahoo, google, etc...

e.g.
menu bar on the left or on the top
functions on the right usually (log in, log out, search, etc)
content usually in the middle/bottom below the logo
logo is a link back to the home page
several links on the bottom like "About" "Careers" "Contact Us" ..etc.