Good news!
I downloaded and played the demo last night on my MacBook Pro (see specs at very top of the thread, graphics card is GeForce 8600M GT)
It ran smoothly with Medium level graphics. High level graphics was locked out... not sure if it was just on my machine or not. There were some issues with pauses before and during cut scenes, but it has been acknowledged by Bioware that these are issues with the demo and will be fixed in the final game.
It's definitely a demo. Lots of stuff is locked out to keep the file size down I suppose. And possibly there will be some areas with more massive fights and performance might be worse, but I am very, very pleasantly surprised by how well it works so far.
I was just wondering what resolution you were playing the game at. I have a Macbook Pro as well from late 2008 with the Core 2 Duo at 2.8, 4 Gb of RAM, and a GeForce 9600M GT. I was running at Medium settings and the game struggled to stick around 30 fps and even then some of the character movements looked glitchy. It should play well on my computer but it wasn't. I'm trying to decide whether to play on the 360 or the PC...I would definitely prefer PC but I was disappointed with the performance on the PC.