I suppose it makes me wonder if my watermark isn't defacing enough (it's moderately translucent). It's certainly visible in all my shots, but I suppose my main concern is, is 640x480 watermarked too high quality? I made the mistake of posting some watermarked images last year on facebook, thinking it was a good and visible way for people to see and order them, and people appropriated them anyway, and I got no orders.
Yeah... so...
Adobe and the BSA like to say that Adobe loses $X billion each year due to Photoshop piracy, and they reach that figure because they simply multiply the number of illegal downloads times the cost of Photoshop. However, this line of reasoning is highly flawed, because in reality, the vast majority of those downloaders were never going to pay $500 for Photoshop, whether they can get it for free or not. That 14 year old kid down the street who downloaded Photoshop to play with does NOT represent $500 in lost sales to Adobe, because that kid doesn't have the means to pay for Photoshop in the first place.
It seems like you're jumping to the conclusion that each person who "stole" your watermarked photo from Facebook represents a lost sale. The fact of the matter is that, whether you posted that image to facebook or not, those people who copied your photo were probably never going to buy your prints in the first place.
Who is the target demographic for your photos? If, for example, the shows you work are concerts that are primarily attended by people in their teens and early 20s, the demographic of potential customers probably don't have the means to pay $15 for a 4x6. They probably don't see the value of paying that much for a print if there is a plethora of free images available on the internet of the same subject/band/etc.
If you aren't selling prints, it doesn't have anything to do with people "stealing" your low-res watermarked images in lieu of buying your prints. You should very carefully consider ways to add value to your work, comapred to what your target demographic can get for free.
Give your photos away for free to as many people as possible to promote your business. Use those images as promotional tools and sell your services directly to the band (etc.) after you've built a reputation for quality.
Just trying to throw some ideas your way to help.. I don't think a more annoying watermark is going to help you sell prints, though.