i wish people would stop making this comparison, because it builds up all sort of unrelated hype. RAGE is not fallout 3. it is also not borderlands. it's been in production longer than either of those games so the whole argument about 'who ripped off who' is moot. imo the game is a tech demo -- hopefully a decent game to boot. it's id's equivalent to crysis. crysis was crap, but the engine was solid. as with tech4 (doom 3, quake 4, prey, etc), i'm sure many other developers will use tech5 to build upon the engine, regardless of whether RAGE will be a good game or not once the SDK gets licensed - or dare i say it - goes public. the real issue here is ultimately the tech5 engine, not the game.
I'd disagree with Crysis being merely a tech demo or it being crap. It was an excellent open world shooter - well, the first half of it anyway, it went downhill during the second half...
I don't expect Rage to be just a tech demo either, they showed off a lot of interesting gameplay elements already, plus they've been working on it for too long for it to be just a pretty engine and nothing more. I imagine they added a lot of content during the last two years, as the engine itself looked and run pretty well years ago.
Also, last time I heard the tech5 engine will only be availabe to other Bethesda/Zenimax devs.