Hey that's pretty cool! I second JoeyD473 -pretty good for just messing around.

If you want to continue it, keep an eye on the style. Its's not a big difference, but you have a cross between flat ( the sea and rivers) and some relief going on there ( the land). Your mountains show more detail on them than the edge of the islands so I would recommend keeping to one 'look' so your map shows consitency. If you want go go the relief side of things, I would say to check out Wilbur. Here's a tutorial as well. it's handy if you want erosion.

Also, in photoshop, you can assign a colour gradient to height. Here's an online tutorial that mentions it. (page 3)

There's also many other cool tutorials in the How to section. different styles that you might prefer.

Keep it up!
thanks for showing it

Cheers
Jez