I've had problems routing too close to the edge of a PCB before and was wondering if there's a suitable rule-of-thumb that I should use (maybe to put in a design rule in Altium somehow with my keepout)? 25mil, 50mil?
I usually do something like 50 mil for planes 100 mil for traces, but it depends on the board house. I usually chamfer the corners of my planes too in case someone drops the board (I've heard that point can make a good radiator too but I've never looked into it).
You should be safe with something like that, but if you look at the house that makes your board I'm sure they have a long list of guidelines that would include this spec. If they don't just send them an email. If they can't answer this question switch board houses ;)
Dave Jones recommends 1mm pullback I believe in his video here: http://www.youtube.com/watch?v=VXE_dh38HjU
I'm sure the "ideal" value varies with boardhouse but that should be a good starting point. There's a ton of other good tips in that video and there's also a Part 2 if you're interested.