i agree totally with rick1337. i am 15 and i am spoiled, but even while i like getting stuff for free, i feel like i dont deserve it. my parents baught us all (me, my brother, my sister) new bikes, (2001 TT-R125Lx2, brother -n- me; 2002 tt-r90, sister) but even while i do feel every bump in the road(weak suspension), i am very grateful for them doing that. today i broke a spoke trying to do a 30' double, (*fyi* i did do it later on, and i am high on life right now because of it;) ) and i am doing the work on it, buying the spoke, and whatnot.
it sounds like you gave him too much, too soon. anyone can make that mistake, and i am sure that i will unconciously do the same thing in a few years, but i am going to put in another vote for Complete Electronic Deprivation (CEP for short.) he will soon see that outdoor/constructive activities will be more appealing to him. i also like the idea someone mentioned about going riding without telling him, and having him see you going and say "hey dad, can i come too?" also have him wrench on the bike while you are wrenching yours, and when he asks "hey dad, whats this do?" you tell him, and if he dosent ask, you ask him. "hey, (son's name), whats this do? if you ask "do you know..." he will be humiliated if he dosent know. but if he pulls the " Gawd, i hate this bike, it sucks, that little kid on a 60 just passed me" then say "well, ya know what? he dosent complain about his bike, he goes out and practices until he's good, you know, better than you. so if you dont want to be shown up by an eight-year-old, you have two choices. either be a quitter and go home, or you can try to get better. if you want to get better, i will help you. if you dont, then just go get in the truck and you can watch me have fun." chances are he will be peed-off and sit and pout in the truck, but next weekend you can pull the "alright, if you think you can be mature about this....." yada yada yada, then you be PATIENT and you will gain his trust. of course it might not work with your son, but it worked with my thirteen-year-old brother, except it was me breaking him down and then building him up. he now tails me around and is getting quite good. i guess its just the thirteenth year that is the most screwy. it was for me and it is for my brother.
holy pickles thats alot of rambling!! sorry about the long post, and may my $0.43 cents help you. ;):)