Here's the thing, personally I don't think watermarks need to be HUGE and placed across the center of the image. My watermark is nice and small, but it's made so that it blends into the image no matter what colors I use for the card. Plus it's difficult to remove easily, even with Photoshop CS!
If you look at the DD gallery (Dirty Dozen gallery) most of those gals have rather small unobtrusive watermarks. To me that's saying something! If the be all and end all artists of SCS aren't marring their cards with these gigantic watermarks, why should you?
I'm not saying you shouldn't have a watermark, especially since SU requires it for web publication, but I'd really rather see the artwork than the watermark!
Here are a couple of samples:
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Which one do you like the best? The tiny one? The HUGE one across the card? Or the one with the initials?