I also really dig RobA's artistic map tut. One thing I've found, though, is that you often end up with pretty clean cut shorelines, which can look odd. I solve this by applying a Displace map (the same thing you would use to make the seashore effect) which roughens up the coastlines a bit. I feel like it makes them a bit more interesting.
Your rivers seem like they're pretty much in the right places (I'm definitely not the river police), though I feel like the bump mapping to bevel them is a bit heavy. Some seem a bit too straight as well. My method for drawing the rivers is usually to use the smallest available brush with the Pencil tool and a spacing of 1. Then draw a fairly meandering line. When I get my rivers in the right places and looking right, you can just Alpha to Selection that layer of thin lines, and grow the selection if you need the rivers to be wider. It can make your rivers a bit longer, but that's nothing you can't solve with a steady hand and the eraser tool if necessary.
I think your blur on the Mountains layer mask is a bit big, and the noise spread RobA mentions in the guide does look good, so you might try that. Your mountain bump mapping seems a bit light, so it might help to duplicate that layer. It would be a good idea to add your rivers to your Dirt layer mask, so that they don't cover up your rivers. The forests and mountains one can buy as covering a body of water, but it's a bit difficult to imagine a beach obscuring an outgoing river.
But yeah, looks good, keep working on it.