According to JR Taylor of Right Wing Trash, director Sam Raimi is Jewish, and there are few things that Jews love more than to support other Jews in their financial endeavors. That was not meant to be quite as snarky as it sounded.
Because now that there are three movies out, we can have a chazakah* about spiderman. For instance, The Libertarian King has been to see every spiderman movie on the opening night. Now, for every spiderman movie ever (unless he specifically commented that he is not going to make a habit of it) he is obligated to go on the opening night.
And of course, Peter Parker, while supposedly not Jewish, is the ultimate nebby* guy. Debbie Schlussel makes the same comment that I did, that Parker cries way too much in the movie. But hey, that's how you know he's sensitive. He's also a math/science genius (focuses on his academics), takes good care of his only living relative, and is so damn broody. Despite his super-powers, Peter Parker is not a manly man.
I could spout a few more traditional stereotypes about ashkenazi* men, but I think that I'll stop here, as you get the idea. And any more will have me sounding like I a) hate Jewish men, and b) am perpetuating anti-Semitic stereotypes. I hate doing that, so I'm going to move on to the last, but not least reason why Jews love Spiderman:
According to MyJewishLearning.com The original comicbook writers were Jewish. The industry was saturated with Jews in the 40's, 50's and 60's. For instance? Stan Lee was born Stanley Martin Leiber, and Jack Kirby was Jacob Kurtzburg. Several major comic book characters are heavily influenced by Jewish tradition, the most obvious of these being the X-man Magneto, who was a concentration camp survivor. NYC's Jewish Museum even had an exhibition on Masters of American Comics.
For all these reasons I'd have you go see Spiderman 3, but there is one reason that you really shouldn't. It isn't that good. 2 hours and 20 minutes of silly, bad dialogue (good fight scenes though), little character development, and random plot. However, if you want to see Topher Grace try to eat Tobey McGuire's head, then this is the movie for you.
*Chazakah: there is a belief that if you do the same thing three times in a row, then you are obligated to do it forever, because it has become your general practice. I don't think that this actually applies to Spiderman movies.
*Nebby is short for nebbish, a Yiddish word which has come to mean the equivalent of a "scrub."
*Ashkenazi Jews are Jews from Europe, generally Caucasian, and their practice of Judaism is the most widely recognized by non-Jews. There are a lot of problems with the hegemony of Ashenazi Jews, but that is a different issue for a different day.