The 2006 course was quite hilly but they changed it last year and, I think, there's more descent than ascent.
You start on Princes Street, which is flat, head out to Holyrood, which is downhill(ish) for two miles. It's then very flat through Edinburgh, out to the sea, before heading out to East Lothian again along flat roads. The course then swings turns back and finishes at Mussleburgh Race Course. Good PB potential.
Scenerey-wise, you take in most of Edinburgh's famous landmarks: Ed Castle, Scott Monument, Arthurs Seat, Holyrood Palace. It then gets quieter once you head out of the city. Going through some of the towns in East Lothian is good as well because all the townsfolk come out and clap for the runners; as they do in the city as well.
There's a discussion thread in the Events section of the forum. I've not contributed myself as yet but I recognise some of the names from last years forum and they're a friendly bunch..