So what exactly goes into revising a book? Do they just plug the errata into it and reprint, or is there actual content change?

Basically, I'm just concerned about buying a book when the New! and Improved! version is coming out fairly soon. If it's just the errata, it's not a big deal, but if the changes are more significant than that, I may consider holding off for a while.

Which books in particular are you talking about? Rigger 3 Revised was a relatively substantial revision [hence the new title] just for the sheer amount of errata that book had. Other ones are usually far more minor. When in doubt, ask, or check the errata on ShadowrunRPG.com.

I'm just waiting for Man & Machine Revised because, honestly, I can't find it anywhere online lately and I need a copy of it to round off the sourcebooks I want...