I doubt it will affect SEO, however this is definitely not the right way to go about this. Instead I propose using one of two methods (There are a few more but I cannot remember them):
In the CSS, use: text-indent: -9999px;
This will make your text go off the screen -9999px; but it will still be read by SEO and by screen readers, the only down side is that on the iPad1 this results in actually making your web page stretch to -9999px too however most designers don’t mind this and therefore its probably the most commonly used method.
Another way is to use: font: 0/0; color: transparent; line-height: 0px;
This is quite a new way and I can’t actually remember the problems to it but I’m sure you’ll be able to google this. I’d personally recommend this way however its up to you.
Oh actually, theres another way for text-indent and you can actually use -100%; instead which defeats the ipad problem I believe.
Im sure you will be able to get someone here to correct me :)
