Hi Phil. Yup, it does look like it's smiling! Very sharp and nice comp. The shallow DOF helps the head stand out from the shell. The light is brighter than ideal - use of a diffusion screen might have helped with that (if the turtle was cooperative). You might try carefully cloning some of the specular highlights around the lower part of the head. Overall, this is very nicely done!
I still have my D50 (sold to me used by my local photography mentor as my first DSLR) and I still use it from time to time. I like the composition, detail and sharpness.... agree with Steve's comments about lighting.
I like this shot too, I don't usually like to mess around too much with the natural content but I wonder if it would be worthwhile disguising the edge of the shell?