How much online support is available for your games of choice? And as a GM, how much mileage do you get out of it?

When I run (or play D&D), I get tons of use out of the online SRD (my version of choice is the one by Sovelior and Sage). I’m also a big fan of having well-designed character sheets — whether official or unoffical — available online. If I were running Burning Wheel, I know I’d be referring back to the Burning Wiki quite often.

Does the presence or absence of online support for a game make a qualitative difference in your enjoyment of GMing that RPG?