Actually no it isnt... to a point.

Alt Tags were actually developed so that those who had poor eyesight or were blind could use the internet.

Basically, the idea behind them was that some software package (the Stephen Hawkins voice ones) would 'read' the web page to a blind surfer thus the Alt Tags would have text in them and, when mouseovered, the surfer would 'hear' what the image and link was for

Just make sure you keep your alt text relevant thats all

Regards,

Lee