I always take mine -ages 2 and 4. The 2 year old never minds and his pictures are pretty sweet -although he always looks bewildered, but my oldest hasn't gone up to Santa or sat in his lap since he was 10m -and now he's 4! We see the same, REALLY great-looking (real beard, nice man) Santa at our neighborhood Winter Wonderland every year (and you get to take your own photos for free), so he should be used to him, but although those 10m photos are fantastic -after that he flipped out about seeing him. He'll go with us, but he waits outside the area where Santa actually is sitting. At age 2, we really wanted a photo of him and his new baby brother, but I had to get in on the action (and I was NOT prepared), so it's pretty awful!
I always urge him to see Santa, but I never "pressure" him. I tell him it's fine and we'll just leave Santa a letter. I think it's fine as long as the kid is okay with it, but forcing a kid who is screaming or scared is mean! I do plan a Christmas card montage in a year or two of all the crazy Santa photos we have of our two and a few of us as kids (that was when all the Santas looked SO fake -and like drunk serial killers with beards!).
Gross and somewhat amusing Santa story -when I was 8 months pregnant with my first child, we were at my husband's company Christmas party. They hired a Santa because at the beginning they had several families and their kids as guests (the kids were all suffering from serious illnesses). They saw Santa, etc. and he stuck around for a bit. He came over and was talking to us and was REALLY, obviously hitting on me! It wasn't in my mind because my husband and two other couples at the table all remarked on it when he walked away. I just felt like, "EWWWWwwwww, Santa has the hots for me and I'm enormously pregnant and he's REALLY old -and, it's Santa!" The guy looked VERY genuine. One of the creepier experiences I've had!