I can personally tell a difference between a 720p source and a 1080p source on my 1080p tv from 9 ft away (40 in. Bravia sony) This is one of the reasons I purchased a 1080P TV.

The difference is especially pronounced when I connect my computer to the television.

However, if you cannot tell a difference from demos for movies, and you do not use your computer with your television, then there is no reason for you to pay the extra money for 1080p.