Well, it'd definitely advance in technology quite fast (I'm very into all that). We'd probably have hover-cars. It would have a unified religion (Christianity). There'd be the unified language of English, except everyone would also dabble in Japanese. We'd all wish we could have a good gaming PC.
Assuming these people were exactly like me, but not me, there wouldn't be the problem of procreation not occuring. Because hey, I'm a horny teenager, as all are.
But I think we'd all get bored of each other pretty quickly, because, while I like to surround myself with intelligent, quirky people, I like there to be quite some disparity between us so we could actually discuss things. When we all have the same views, even the most intricate discussions would come down to "Yep, I agree."
Unfortunately, we'd all look like Hitler's Aryans, and not wanting to let Hitler win, we'd probably have a mass suicide (jokes, I'm completely against suicide on every level).
The government would probably consist of some dude in an office saying "Yeah, I'll give you a permit for that, do what you want." The world would also go through cycles of being completely messy and unorganised to ridiculously clean and well-kept. Whenever they want to put off doing something (like reconstructing civilisation to suit this unified populace) they'd all procrastinate and start cleaning things, ending up with a very clean world.
Okay that's all I've got for now.