Asking a computer to check aesthetics is start of your descent into madness. Use Selenium to check that links do what you expect, elements are loaded etc. Don't use it to check if a button graphic has the right icon loaded.
Computers are great at functional testing but you still a Mk1 eyeball to check aesthetics. Luckily, functionality is what your customers will really care about. No one will shout at you if an element is misaligned for a while before you catch it with manual testing
Side note -- I definitely agree about not using Selenium to check for alignment, images loading, etc..
But... it's pretty cool to have a single Selenium test that does nothing but zip through your site and show all of the unique views at rapid fire speed, so as soon as the page is loaded it has already filled in any relevant form and is loading the next page.
Make sure someone with good concentration sits and watches that test run once in a while; anything seriously wrong will pop out, and they can watch it zip along while taking a coffee break.
Computers are great at functional testing but you still a Mk1 eyeball to check aesthetics. Luckily, functionality is what your customers will really care about. No one will shout at you if an element is misaligned for a while before you catch it with manual testing