This is why people hate Macs... The users!
All he's after is some advice, he didn't say he wouldn't use the machine a lot except that he doesn't overly need a LAPTOP except for when on holidays or around a friends.
I have both, and would recommend the MacBook over the iMac purely as that was the order i brought mine (with money i worked for web designing aged 14) and i love the portability of the MacBook, although my new 24" 3.06 is a beast!
The OP is three years younger than me and I'm as adult as it gets, 18 on the outside but mentally about 35. I'm working full time instead of going to Uni, even though i got more than enough grades to get in, as i feel that Uni is a complete waste of time and money and wish to get on the housing market... You're as adult as your mind makes you!