Hee thanks! Um - I just make them in Photoshop lol, there's not much more to it! I tend to use filters a lot - I use the Mr. Retro Machine Wash filters a lot, as well as various Alien Skin plugins, and let's not forget some of the stuff in the Resources section of deviantArt. I also just draw a lot of stuff, using the pen tool and/or custom shapes, and then run filters over whatever I've drawn to make it look faded/vintage/metallic/plastic/whatever fits the rest of the wallpaper.
No secret tips or anything - just a lot of time, really! On average, it takes me about 3 or 4 hours to finish one wallpaper (though often enough I've spent closer to 6), and they usually have at least 20 or 30 layers.
The layouts I make myself, see above. But some of patterns are indeed based on scrapbooking stuff! A bunch of my friends are scrapbook designers.
Glad you all like them - hearing that always motivates me to make more!