I know in flintknapping sometimes it's a good idea to bake certain types of rocks to make them more workable and break more predictably, but I got hold of some really fissile obsidian that tends to shatter more than flake and I was wondering if it was common or acceptable practice (or safe, for that matter) to bake obsidian to make it flake better and how would I go about it?

It really depends on water content as to whether it's safe or not.  I've never really used obsidian, so I don't know much about the water content in it.  I know that most flints and cherts typically have quite a lot of water in, and will often just shatter or explode when heated.  I'd say go and ask someone on PaleoPlanet.  Sorry I couldn't help.

Actually, obsidian is a working material that you don't need to heat treat.  I suspect what you got on had is just bad obsidian (well, for knapping, anyway)...remember, obsidian is a glass, made in volcanoes, and the problem might not be water at all, but the gasous composition of your material...the Obisidian Spirit did not create all obsidian to be equal. 

Speaking for myself, I prefer to use obsidian (from www.neolithics.com) or glass.  When I get flint, it's already heat treated, which is a slow process of bringing the heat up slooowly, and bringing it down slooowly.  Otherwise, you get...gravel.  For much more info than you could ever think of using, consult my friends at...http://groups.yahoo.com/group/TheTarp

Caveman Bob