If you plan to dine at either of Emeril's restaurants, a reservation is mandatory. Book as far ahead as possible. They fill up fast. Reservations at The Palm & Bice aren't as hard to get, but they can also be made at the following link:
http://www.opentable.com/start.aspx?m=28&n=64
Reservations for Hard Rock Cafe can be made at the following link or by calling 1-407-224-FOOD:
https://www.hardrock.com/px/px/register.asp?
selLocation=ORLANDO
NBA City reservations:
http://www.nba.com/nbacity/index.html
1-407-224-9255 - Number for making reservations at restaurants in Universal Parks & Resorts (excluding Emeril's)
1-407-224-2155 - Margaritaville
1-407-224-FOOD - Bob Marley, Pat O'Briens, Latin Quarter, & Pastamore
The number for Bubba Gump is 1-407-903-0044, but I'm not sure if they're taking reservations yet or not.
1-407-224-7223 is the number for Nascar Sports Grille. It has been recently redone. Like Bubba Gump, I'm not sure if they're taking reservations yet.
Some of the restaurants (i.e. Mythos) don't finalize schedules or take reservations, until around 2 weeks in advance.
You can also make same day reservations at kiosks at CityWalk & in the parks.
Note: Some of the restaurants take reservations. Some take priority seating, which is pretty much the same as having a reservation.