I like it but I do most of my initial design on good old fashioned graph paper. Pretty much like PaperPrincess described - I move them into EQ7 after I've settled on at least the basic format for the quilt.
I use it mostly to try out different fabric colors. And also just to play.
I don't think it's a NECESSARY tool, especially if you're comfortable with doing things "manually". But it's fun and can lead to some surprising designs when you're absent-mindedly flipping blocks around.
But also....there are some things I can't figure out how to draw in EQ7 that are easy to draw on graph paper. Might just be that I haven't figured it out yet - the software does have a learning curve.