I don't agree with the if the baby is looking interested at what you're doing (eating) they're ready to start.
How about, if the baby is not settling as easily, or seeming to not be satisfied with just milk anymore, then they are ready for solids. My kids were ALWAYS interested in what I was doing. Whether it be eating a carrot, or drinking a beer, they were wanting to grab it. Doesn't mean I gave it to them.
[Edited on 18/06/2008]