Returning to a "warm" macbook pro that was "idle"

well, I just left my macbook pro open (running mail, ichat and firefox) while enjoying dinner with the family, came back to check something (woke it up) and noticed that it's quite warm above the keyboard.

Is this normal?

I took a snap of the activity monitor and is that much of the CPU supposed to be used when running nothing?

Doesn't look like much of the CPU is used at all. But since Activity Monitor isn't sorted by CPU utilization in your screenshot, it's kind of hard to same.

As far as heat goes, since the casing is aluminum, it acts as a heatsink and anytime any of the heat generating components has electrons running through it, it can get warm. In short, I don't think you have anything to worry about.

Your System processes were taking up 31% of your CPU (mine hovers around 4%), so click the drop-down menu where it says 'My Processes' - then select 'System Processes' - then double click the CPU column header, and you'll see which process is doing the work. Google that process and you should be closer to an answer.